diff --git a/src/coordinators/gameLogCoordinator.js b/src/coordinators/gameLogCoordinator.js
index ebd7b2b0..8f9fb137 100644
--- a/src/coordinators/gameLogCoordinator.js
+++ b/src/coordinators/gameLogCoordinator.js
@@ -88,7 +88,8 @@ export async function tryLoadPlayerList() {
                     ctx.userId =
                         findUserByDisplayName(
                             userStore.cachedUsers,
-                            ctx.displayName
+                            ctx.displayName,
+                            userStore.cachedUserIdsByDisplayName
                         )?.id ?? '';
                 }
                 const userMap = {
@@ -159,8 +160,11 @@ export function addGameLogEntry(gameLog, location) {
     let userId = String(gameLog.userId || '');
     if (!userId && gameLog.displayName) {
         userId =
-            findUserByDisplayName(userStore.cachedUsers, gameLog.displayName)
-                ?.id ?? '';
+            findUserByDisplayName(
+                userStore.cachedUsers,
+                gameLog.displayName,
+                userStore.cachedUserIdsByDisplayName
+            )?.id ?? '';
     }
     switch (gameLog.type) {
         case 'location-destination':
@@ -408,7 +412,8 @@ export function addGameLogEntry(gameLog, location) {
             if (typeof ref2 === 'undefined') {
                 const foundUser = findUserByDisplayName(
                     userStore.cachedUsers,
-                    gameLog.displayName
+                    gameLog.displayName,
+                    userStore.cachedUserIdsByDisplayName
                 );
                 if (foundUser) {
                     photonStore.photonLobby.set(photonId, foundUser);
diff --git a/src/coordinators/userCoordinator.js b/src/coordinators/userCoordinator.js
index 7c3f9a82..d597d1d9 100644
--- a/src/coordinators/userCoordinator.js
+++ b/src/coordinators/userCoordinator.js
@@ -80,11 +80,14 @@ export function applyUser(json) {
         cachedUsers,
         currentTravelers,
         customUserTags,
+        rebuildCachedUserDisplayNameIndex,
+        setCachedUser,
         state,
         userDialog
     } = userStore;
 
     let ref = cachedUsers.get(json.id);
+    let previousDisplayName = '';
     let hasPropChanged = false;
     let changedProps = {};
     sanitizeUserJson(json, getRobotUrl());
@@ -111,18 +114,24 @@ export function applyUser(json) {
             ref.$customTag = '';
             ref.$customTagColour = '';
         }
-        evictMapCache(
+        const { deletedCount } = evictMapCache(
             cachedUsers,
             friendStore.friends.size + 300,
             (_value, key) => friendStore.friends.has(key),
             { logLabel: 'User cache cleanup' }
         );
-        cachedUsers.set(ref.id, ref);
+        if (deletedCount > 0) {
+            setCachedUser(ref, '', { skipIndex: true });
+            rebuildCachedUserDisplayNameIndex();
+        } else {
+            setCachedUser(ref);
+        }
         runUpdateFriendFlow(ref.id);
     } else {
         if (json.state !== 'online') {
             runUpdateFriendFlow(ref.id, json.state);
         }
+        previousDisplayName = ref.displayName;
         const { hasPropChanged: _hasPropChanged, changedProps: _changedProps } =
             diffObjectProps(ref, json, arraysMatch);
         for (const prop in json) {
@@ -130,6 +139,7 @@ export function applyUser(json) {
                 ref[prop] = json[prop];
             }
         }
+        setCachedUser(ref, previousDisplayName);
         hasPropChanged = _hasPropChanged;
         changedProps = _changedProps;
     }
@@ -637,7 +647,11 @@ export async function lookupUser(ref) {
     if (!ref.displayName || ref.displayName.substring(0, 3) === 'ID:') {
         return;
     }
-    const found = findUserByDisplayName(userStore.cachedUsers, ref.displayName);
+    const found = findUserByDisplayName(
+        userStore.cachedUsers,
+        ref.displayName,
+        userStore.cachedUserIdsByDisplayName
+    );
     if (found) {
         showUserDialog(found.id);
         return;
diff --git a/src/coordinators/userSessionCoordinator.js b/src/coordinators/userSessionCoordinator.js
index 332d8d7c..340bcedd 100644
--- a/src/coordinators/userSessionCoordinator.js
+++ b/src/coordinators/userSessionCoordinator.js
@@ -51,7 +51,7 @@ export function runFirstLoginFlow(ref, { now = Date.now } = {}) {
     if (gameStore.isGameRunning) {
         ref.$previousAvatarSwapTime = now();
     }
-    userStore.cachedUsers.clear(); // clear before running applyUser
+    userStore.clearCachedUsers(); // clear before running applyUser
     userStore.setCurrentUser(ref);
     authStore.loginComplete();
 }
diff --git a/src/coordinators/vrcxCoordinator.js b/src/coordinators/vrcxCoordinator.js
index d2448c99..1f13e501 100644
--- a/src/coordinators/vrcxCoordinator.js
+++ b/src/coordinators/vrcxCoordinator.js
@@ -35,7 +35,7 @@ export function clearVRCXCache() {
             !locationStore.lastLocation.playerList.has(ref.id) &&
             id !== userStore.currentUser.id
         ) {
-            userStore.cachedUsers.delete(id);
+            userStore.deleteCachedUser(id);
         }
     });
     worldStore.cachedWorlds.forEach((ref, id) => {
diff --git a/src/shared/utils/__tests__/user.findByDisplayName.test.js b/src/shared/utils/__tests__/user.findByDisplayName.test.js
index 3fb4cef2..65e07156 100644
--- a/src/shared/utils/__tests__/user.findByDisplayName.test.js
+++ b/src/shared/utils/__tests__/user.findByDisplayName.test.js
@@ -17,6 +17,19 @@ describe('findUserByDisplayName', () => {
         return map;
     }
 
+    function createDisplayNameIndex(entries) {
+        const index = new Map();
+        for (const entry of entries) {
+            let ids = index.get(entry.displayName);
+            if (!ids) {
+                ids = new Set();
+                index.set(entry.displayName, ids);
+            }
+            ids.add(entry.id);
+        }
+        return index;
+    }
+
     test('returns the user matching displayName', () => {
         const users = createCachedUsers([
             { id: 'usr_1', displayName: 'Alice' },
@@ -56,4 +69,31 @@ describe('findUserByDisplayName', () => {
         expect(findUserByDisplayName(users, 'alice')).toBeUndefined();
         expect(findUserByDisplayName(users, 'ALICE')).toBeUndefined();
     });
+
+    test('uses displayName index when provided', () => {
+        const entries = [
+            { id: 'usr_1', displayName: 'Alice' },
+            { id: 'usr_2', displayName: 'Bob' }
+        ];
+        const users = createCachedUsers(entries);
+        const index = createDisplayNameIndex(entries);
+
+        const result = findUserByDisplayName(users, 'Bob', index);
+
+        expect(result).toEqual({ id: 'usr_2', displayName: 'Bob' });
+    });
+
+    test('indexed lookup falls back to next duplicate when first user is missing', () => {
+        const entries = [
+            { id: 'usr_1', displayName: 'Alice' },
+            { id: 'usr_2', displayName: 'Alice' }
+        ];
+        const users = createCachedUsers(entries);
+        users.delete('usr_1');
+        const index = createDisplayNameIndex(entries);
+
+        const result = findUserByDisplayName(users, 'Alice', index);
+
+        expect(result).toEqual({ id: 'usr_2', displayName: 'Alice' });
+    });
 });
diff --git a/src/shared/utils/user.js b/src/shared/utils/user.js
index 79d0d593..187217e9 100644
--- a/src/shared/utils/user.js
+++ b/src/shared/utils/user.js
@@ -275,9 +275,23 @@ function userOnlineFor(ref) {
  * Find a user object from cachedUsers by displayName.
  * @param {Map} cachedUsers
  * @param {string} displayName
+ * @param {Map<string, Set<string>>} [cachedUserIdsByDisplayName]
  * @returns {object|undefined}
  */
-function findUserByDisplayName(cachedUsers, displayName) {
+function findUserByDisplayName(
+    cachedUsers,
+    displayName,
+    cachedUserIdsByDisplayName
+) {
+    const indexedUserIds = cachedUserIdsByDisplayName?.get(displayName);
+    if (indexedUserIds) {
+        for (const userId of indexedUserIds) {
+            const ref = cachedUsers.get(userId);
+            if (ref?.displayName === displayName) {
+                return ref;
+            }
+        }
+    }
     for (const ref of cachedUsers.values()) {
         if (ref.displayName === displayName) {
             return ref;
diff --git a/src/stores/gameLog/index.js b/src/stores/gameLog/index.js
index 0305338c..16ac5046 100644
--- a/src/stores/gameLog/index.js
+++ b/src/stores/gameLog/index.js
@@ -193,7 +193,8 @@ export const useGameLogStore = defineStore('GameLog', () => {
                 ctx.userId =
                     findUserByDisplayName(
                         userStore.cachedUsers,
-                        ctx.displayName
+                        ctx.displayName,
+                        userStore.cachedUserIdsByDisplayName
                     )?.id ?? '';
             }
             notificationStore.queueGameLogNoty(ctx);
diff --git a/src/stores/gameLog/mediaParsers.js b/src/stores/gameLog/mediaParsers.js
index 8d2765d2..3e69694e 100644
--- a/src/stores/gameLog/mediaParsers.js
+++ b/src/stores/gameLog/mediaParsers.js
@@ -139,8 +139,11 @@ export function createMediaParsers({
         let userId = '';
         if (displayName) {
             userId =
-                findUserByDisplayName(userStore.cachedUsers, displayName)?.id ??
-                '';
+                findUserByDisplayName(
+                    userStore.cachedUsers,
+                    displayName,
+                    userStore.cachedUserIdsByDisplayName
+                )?.id ?? '';
         }
         if (videoId === 'YouTube') {
             const entry1 = {
@@ -207,8 +210,11 @@ export function createMediaParsers({
         let userId = '';
         if (displayName) {
             userId =
-                findUserByDisplayName(userStore.cachedUsers, displayName)?.id ??
-                '';
+                findUserByDisplayName(
+                    userStore.cachedUsers,
+                    displayName,
+                    userStore.cachedUserIdsByDisplayName
+                )?.id ?? '';
         }
         if (videoId === 'YouTube') {
             const entry1 = {
@@ -270,8 +276,11 @@ export function createMediaParsers({
         let userId = '';
         if (displayName) {
             userId =
-                findUserByDisplayName(userStore.cachedUsers, displayName)?.id ??
-                '';
+                findUserByDisplayName(
+                    userStore.cachedUsers,
+                    displayName,
+                    userStore.cachedUserIdsByDisplayName
+                )?.id ?? '';
         }
         if (videoId === 'YouTube') {
             const entry1 = {
@@ -327,8 +336,11 @@ export function createMediaParsers({
         let userId = '';
         if (displayName) {
             userId =
-                findUserByDisplayName(userStore.cachedUsers, displayName)?.id ??
-                '';
+                findUserByDisplayName(
+                    userStore.cachedUsers,
+                    displayName,
+                    userStore.cachedUserIdsByDisplayName
+                )?.id ?? '';
         }
         const entry1 = {
             created_at: gameLog.dt,
@@ -384,8 +396,11 @@ export function createMediaParsers({
         let userId = '';
         if (displayName) {
             userId =
-                findUserByDisplayName(userStore.cachedUsers, displayName)?.id ??
-                '';
+                findUserByDisplayName(
+                    userStore.cachedUsers,
+                    displayName,
+                    userStore.cachedUserIdsByDisplayName
+                )?.id ?? '';
         }
         const entry1 = {
             created_at: gameLog.dt,
diff --git a/src/stores/notification/index.js b/src/stores/notification/index.js
index f862d2fb..80adb9af 100644
--- a/src/stores/notification/index.js
+++ b/src/stores/notification/index.js
@@ -1018,8 +1018,11 @@ export const useNotificationStore = defineStore('Notification', () => {
         if (id) return id;
         if (noty.displayName) {
             return (
-                findUserByDisplayName(userStore.cachedUsers, noty.displayName)
-                    ?.id ?? ''
+                findUserByDisplayName(
+                    userStore.cachedUsers,
+                    noty.displayName,
+                    userStore.cachedUserIdsByDisplayName
+                )?.id ?? ''
             );
         }
         return '';
@@ -1086,7 +1089,8 @@ export const useNotificationStore = defineStore('Notification', () => {
         } else if (noty.displayName) {
             const ref = findUserByDisplayName(
                 userStore.cachedUsers,
-                noty.displayName
+                noty.displayName,
+                userStore.cachedUserIdsByDisplayName
             );
             if (ref) {
                 noty.isFriend = friendStore.friends.has(ref.id);
diff --git a/src/stores/user.js b/src/stores/user.js
index 28507399..7d681ddb 100644
--- a/src/stores/user.js
+++ b/src/stores/user.js
@@ -271,6 +271,78 @@ export const useUserStore = defineStore('User', () => {
     });
 
     const cachedUsers = shallowReactive(new Map());
+    const cachedUserIdsByDisplayName = shallowReactive(new Map());
+
+    function addCachedUserDisplayNameEntry(displayName, userId) {
+        if (!displayName || !userId) {
+            return;
+        }
+        let userIds = cachedUserIdsByDisplayName.get(displayName);
+        if (!userIds) {
+            userIds = new Set();
+            cachedUserIdsByDisplayName.set(displayName, userIds);
+        }
+        userIds.add(userId);
+    }
+
+    function removeCachedUserDisplayNameEntry(displayName, userId) {
+        if (!displayName || !userId) {
+            return;
+        }
+        const userIds = cachedUserIdsByDisplayName.get(displayName);
+        if (!userIds) {
+            return;
+        }
+        userIds.delete(userId);
+        if (userIds.size === 0) {
+            cachedUserIdsByDisplayName.delete(displayName);
+        }
+    }
+
+    function syncCachedUserDisplayName(ref, previousDisplayName = '') {
+        if (!ref?.id) {
+            return;
+        }
+        if (previousDisplayName && previousDisplayName !== ref.displayName) {
+            removeCachedUserDisplayNameEntry(previousDisplayName, ref.id);
+        }
+        addCachedUserDisplayNameEntry(ref.displayName, ref.id);
+    }
+
+    function setCachedUser(
+        ref,
+        previousDisplayName = '',
+        { skipIndex = false } = {}
+    ) {
+        if (!ref?.id) {
+            return;
+        }
+        cachedUsers.set(ref.id, ref);
+        if (!skipIndex) {
+            syncCachedUserDisplayName(ref, previousDisplayName);
+        }
+    }
+
+    function deleteCachedUser(userId) {
+        const ref = cachedUsers.get(userId);
+        if (!ref) {
+            return false;
+        }
+        removeCachedUserDisplayNameEntry(ref.displayName, userId);
+        return cachedUsers.delete(userId);
+    }
+
+    function clearCachedUsers() {
+        cachedUsers.clear();
+        cachedUserIdsByDisplayName.clear();
+    }
+
+    function rebuildCachedUserDisplayNameIndex() {
+        cachedUserIdsByDisplayName.clear();
+        for (const ref of cachedUsers.values()) {
+            addCachedUserDisplayNameEntry(ref.displayName, ref.id);
+        }
+    }
 
     const isLocalUserVrcPlusSupporter = computed(
         () => currentUser.value.$isVRCPlus || AppDebug.debugVrcPlus
@@ -730,10 +802,16 @@ export const useUserStore = defineStore('User', () => {
         showUserDialogHistory,
         customUserTags,
         cachedUsers,
+        cachedUserIdsByDisplayName,
         isLocalUserVrcPlusSupporter,
         applyUserLanguage,
         applyPresenceLocation,
         applyUserDialogLocation,
+        setCachedUser,
+        syncCachedUserDisplayName,
+        deleteCachedUser,
+        clearCachedUsers,
+        rebuildCachedUserDisplayNameIndex,
         sortUserDialogAvatars,
         initUserNotes,
         showSendBoopDialog,