diff --git a/src/stores/AsyncStoreWithClient.ts b/src/stores/AsyncStoreWithClient.ts
index 4accef6f77..1ed7c6a547 100644
--- a/src/stores/AsyncStoreWithClient.ts
+++ b/src/stores/AsyncStoreWithClient.ts
@@ -48,7 +48,10 @@ export abstract class AsyncStoreWithClient<T extends Object> extends AsyncStore<
         await this.onAction(payload);
 
         if (payload.action === 'MatrixActions.sync') {
-            // Filter out anything that isn't the first PREPARED sync.
+            // Only set the client on the transition into the PREPARED state.
+            // Everything after this is unnecessary (we only need to know once we have a client)
+            // and we intentionally don't set the client before this point to avoid stores
+            // updating for every event emitted during the cached sync.
             if (!(payload.prevState === 'PREPARED' && payload.state !== 'PREPARED')) {
                 return;
             }
diff --git a/src/stores/BreadcrumbsStore.ts b/src/stores/BreadcrumbsStore.ts
index 34affbe746..ea29cb9dfc 100644
--- a/src/stores/BreadcrumbsStore.ts
+++ b/src/stores/BreadcrumbsStore.ts
@@ -55,7 +55,7 @@ export class BreadcrumbsStore extends AsyncStoreWithClient<IState> {
     }
 
     private get meetsRoomRequirement(): boolean {
-        return this.matrixClient.getVisibleRooms().length >= 20;
+        return this.matrixClient && this.matrixClient.getVisibleRooms().length >= 20;
     }
 
     protected async onAction(payload: ActionPayload) {