Put back code

with comment hopefully explaining why it's necessary

src/stores/AsyncStoreWithClient.ts

@@ -35,6 +35,13 @@ export abstract class AsyncStoreWithClient<T extends Object> extends AsyncStore<
         await this.onAction(payload);
 
         if (payload.action === 'MatrixActions.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;
+            }
             this.matrixClient = payload.matrixClient;
             await this.onReady();
         } else if (payload.action === 'on_client_not_viable' || payload.action === 'on_logged_out') {