diff --git a/src/room/GroupCallView.test.tsx b/src/room/GroupCallView.test.tsx
index 1c4f2462a..92c27077f 100644
--- a/src/room/GroupCallView.test.tsx
+++ b/src/room/GroupCallView.test.tsx
@@ -38,7 +38,6 @@ import { useAudioContext } from "../useAudioContext";
 import { ActiveCall } from "./InCallView";
 import {
   flushPromises,
-  mockConfig,
   mockEmitter,
   mockMatrixRoom,
   mockMatrixRoomMember,
@@ -51,7 +50,6 @@ import { GroupCallErrorBoundary } from "./GroupCallErrorBoundary";
 import { ElementWidgetActions, type WidgetHelpers } from "../widget";
 import { LazyEventEmitter } from "../LazyEventEmitter";
 import { MatrixRTCTransportMissingError } from "../utils/errors";
-import { MatrixRTCMode } from "../config/ConfigOptions";
 import { ProcessorProvider } from "../livekit/TrackProcessorContext";
 import { MediaDevicesContext } from "../MediaDevicesContext";
 import { constant } from "../state/Behavior";
@@ -134,7 +132,6 @@ function createGroupCallView(
   widget: WidgetHelpers | null,
   joined = true,
   options: {
-    doesServerSupportUnstableFeature?: (feature: string) => Promise<boolean>;
     withErrorBoundary?: boolean;
   } = {},
 ): {
@@ -146,9 +143,6 @@ function createGroupCallView(
     getUserId: () => localRtcMember.userId,
     getDeviceId: () => localRtcMember.deviceId,
     getRoom: (rId) => (rId === roomId ? room : null),
-    doesServerSupportUnstableFeature:
-      options.doesServerSupportUnstableFeature ??
-      vi.fn().mockResolvedValue(true),
   } as Partial<MatrixClient> as MatrixClient;
   const room = mockMatrixRoom({
     relations: {
@@ -416,28 +410,37 @@ test.skip("GroupCallView shows errors that occur during joining", async () => {
   screen.getByText("Call is not supported");
 });
 
-test("shows StickyEventsRequiredError when matrix_2_0 is forced but homeserver lacks MSC4354", async () => {
-  mockConfig({ matrix_rtc_mode: MatrixRTCMode.Matrix_2_0 });
-  createGroupCallView(null, true, {
-    doesServerSupportUnstableFeature: vi.fn().mockResolvedValue(false),
+test("translates UnsupportedStickyEventsEndpointError to the StickyEventsRequiredError screen", async () => {
+  // Match the shape the SDK emits on
+  // MatrixRTCSessionEvent.MembershipManagerError when matrix_2_0 mode is
+  // configured but the homeserver does not advertise MSC4354.
+  const stickyError = new Error("Server does not support the sticky events");
+  stickyError.name = "UnsupportedStickyEventsEndpointError";
+
+  const { rtcSession } = createGroupCallView(null, true, {
     withErrorBoundary: true,
   });
+
+  await act(() =>
+    rtcSession.emit(MatrixRTCSessionEvent.MembershipManagerError, stickyError),
+  );
+
   await screen.findByText("Homeserver does not support Matrix 2.0 calls");
 });
 
-test("does not show StickyEventsRequiredError when homeserver supports MSC4354", async () => {
-  mockConfig({ matrix_rtc_mode: MatrixRTCMode.Matrix_2_0 });
-  const { getByText } = createGroupCallView(null, true, {
-    doesServerSupportUnstableFeature: vi.fn().mockResolvedValue(true),
+test("falls back to ConnectionLostError for unrecognised membership manager errors", async () => {
+  const { rtcSession } = createGroupCallView(null, true, {
     withErrorBoundary: true,
   });
-  // Give the async support check a chance to resolve.
-  await flushPromises();
-  expect(
-    screen.queryByText("Homeserver does not support Matrix 2.0 calls"),
-  ).toBeNull();
-  // The normal call UI (mocked ActiveCall) renders instead.
-  expect(getByText("Leave")).toBeInTheDocument();
+
+  await act(() =>
+    rtcSession.emit(
+      MatrixRTCSessionEvent.MembershipManagerError,
+      new Error("something else broke"),
+    ),
+  );
+
+  await screen.findByText("Connection lost");
 });
 
 test("user can reconnect after a membership manager error", async () => {
diff --git a/src/room/GroupCallView.tsx b/src/room/GroupCallView.tsx
index 7fa47551e..0879efda8 100644
--- a/src/room/GroupCallView.tsx
+++ b/src/room/GroupCallView.tsx
@@ -13,12 +13,7 @@ import {
   useMemo,
   useState,
 } from "react";
-import {
-  type MatrixClient,
-  JoinRule,
-  type Room,
-  UNSTABLE_MSC4354_STICKY_EVENTS,
-} from "matrix-js-sdk";
+import { type MatrixClient, JoinRule, type Room } from "matrix-js-sdk";
 import {
   Room as LivekitRoom,
   isE2EESupported as isE2EESupportedBrowser,
@@ -75,8 +70,6 @@ import {
   StickyEventsRequiredError,
   UnknownCallError,
 } from "../utils/errors.ts";
-import { Config } from "../config/Config.ts";
-import { MatrixRTCMode } from "../config/ConfigOptions.ts";
 import { GroupCallErrorBoundary } from "./GroupCallErrorBoundary.tsx";
 import { useTypedEventEmitter } from "../useEvents";
 import { muteAllAudio$ } from "../state/MuteAllAudioModel.ts";
@@ -170,30 +163,21 @@ export const GroupCallView: FC<Props> = ({
   useTypedEventEmitter(
     rtcSession,
     MatrixRTCSessionEvent.MembershipManagerError,
-    (error) => setExternalError(new ConnectionLostError()),
+    (error) => {
+      // The SDK throws this typed error when matrix_rtc_mode=matrix_2_0 is in
+      // effect but the homeserver does not advertise MSC4354 (sticky events).
+      // Surface the actual cause instead of a generic connection-lost screen.
+      if (
+        error instanceof Error &&
+        error.name === "UnsupportedStickyEventsEndpointError"
+      ) {
+        setExternalError(new StickyEventsRequiredError());
+      } else {
+        setExternalError(new ConnectionLostError());
+      }
+    },
   );
 
-  // If the deployment pins matrix_rtc_mode=matrix_2_0 but this homeserver
-  // doesn't advertise MSC4354 (sticky events), the call will fail to connect
-  // with a generic "Connection lost" message. Surface the real cause up front.
-  useEffect(() => {
-    if (Config.get().matrix_rtc_mode !== MatrixRTCMode.Matrix_2_0) return;
-    let cancelled = false;
-    client
-      .doesServerSupportUnstableFeature(UNSTABLE_MSC4354_STICKY_EVENTS)
-      .then((supported) => {
-        if (!cancelled && !supported) {
-          setExternalError(new StickyEventsRequiredError());
-        }
-      })
-      .catch((e) => {
-        logger.warn("Failed to check sticky-events homeserver support", e);
-      });
-    return (): void => {
-      cancelled = true;
-    };
-  }, [client]);
-
   useEffect(() => {
     // Sanity check the room object
     if (client.getRoom(rtcSession.room.roomId) !== rtcSession.room)