diff --git a/ui/src/pages/debug/debug-page.ts b/ui/src/pages/debug/debug-page.ts
index 5c859d6e5715..51a1c292fcd1 100644
--- a/ui/src/pages/debug/debug-page.ts
+++ b/ui/src/pages/debug/debug-page.ts
@@ -1,6 +1,6 @@
 import { consume } from "@lit/context";
 import { initialState, Task, TaskStatus } from "@lit/task";
-import { html } from "lit";
+import { html, nothing } from "lit";
 import { state } from "lit/decorators.js";
 import type { EventLogEntry } from "../../api/event-log.ts";
 import type { GatewayBrowserClient } from "../../api/gateway.ts";
@@ -34,6 +34,7 @@ class DebugPage extends OpenClawLightDomElement {
   @state() private debugCallParams = "{}";
   @state() private debugCallResult: string | null = null;
   @state() private debugCallError: string | null = null;
+  @state() private debugDiagnosticsError: string | null = null;
   @state() private eventLog: readonly EventLogEntry[] = [];
 
   private readonly polling = new PollController(
@@ -55,6 +56,7 @@ class DebugPage extends OpenClawLightDomElement {
       client ? loadGatewayDiagnostics(client, signal) : initialState,
     onComplete: (result) => {
       this.diagnosticsTaskActiveClient = null;
+      this.debugDiagnosticsError = null;
       this.debugStatus = result.status;
       this.debugHealth = result.health;
       this.debugModels = result.models;
@@ -62,7 +64,7 @@ class DebugPage extends OpenClawLightDomElement {
     },
     onError: (error) => {
       this.diagnosticsTaskActiveClient = null;
-      this.debugCallError = String(error);
+      this.debugDiagnosticsError = String(error);
     },
   });
   private readonly subscriptions = new SubscriptionsController(this)
@@ -122,6 +124,7 @@ class DebugPage extends OpenClawLightDomElement {
     this.debugHeartbeat = null;
     this.debugCallResult = null;
     this.debugCallError = null;
+    this.debugDiagnosticsError = null;
   }
 
   private syncPolling() {
@@ -156,7 +159,7 @@ class DebugPage extends OpenClawLightDomElement {
     this.debugCallError = null;
     this.debugCallResult = null;
     const gateway = this.gatewaySource;
-    const epoch = this.callEpoch;
+    const epoch = ++this.callEpoch;
     const isCurrent = () =>
       this.connected &&
       this.client === client &&
@@ -179,7 +182,7 @@ class DebugPage extends OpenClawLightDomElement {
   }
 
   override render() {
-    const body = renderDebug({
+    const debugView = renderDebug({
       loading: this.diagnosticsTask.status === TaskStatus.PENDING,
       status: this.debugStatus,
       health: this.debugHealth,
@@ -196,6 +199,12 @@ class DebugPage extends OpenClawLightDomElement {
       onRefresh: () => void this.loadDiagnostics(),
       onCall: () => void this.callDebugMethod(),
     });
+    const body = html`
+      ${this.debugDiagnosticsError
+        ? html`<div class="callout danger" role="alert">${this.debugDiagnosticsError}</div>`
+        : nothing}
+      ${debugView}
+    `;
     return html`
       <section class="content-header">
         <div>
diff --git a/ui/src/pages/debug/view.test.ts b/ui/src/pages/debug/view.test.ts
index 68008ddee92f..0aa8536f5bce 100644
--- a/ui/src/pages/debug/view.test.ts
+++ b/ui/src/pages/debug/view.test.ts
@@ -1,11 +1,82 @@
 // Control UI tests cover debug behavior.
 import { render } from "lit";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import type { GatewayBrowserClient } from "../../api/gateway.ts";
+import type { ApplicationContext, ApplicationGatewaySnapshot } from "../../app/context.ts";
 import { i18n } from "../../i18n/index.ts";
 import { createStorageMock } from "../../test-helpers/storage.ts";
+import "./debug-page.ts";
 import { renderDebug } from "./view.ts";
 
 type DebugProps = Parameters<typeof renderDebug>[0];
+type TestDebugPage = HTMLElement & {
+  context: ApplicationContext;
+  debugCallError: string | null;
+  debugCallMethod: string;
+  debugCallResult: string | null;
+  debugStatus: unknown;
+  loadDiagnostics: () => Promise<void>;
+  requestUpdate: () => void;
+  updateComplete: Promise<boolean>;
+};
+
+function deferred<T>() {
+  let resolve!: (value: T) => void;
+  let reject!: (reason?: unknown) => void;
+  const promise = new Promise<T>((nextResolve, nextReject) => {
+    resolve = nextResolve;
+    reject = nextReject;
+  });
+  return { promise, resolve, reject };
+}
+
+async function mountDebugPage(
+  request: (method: string) => Promise<unknown>,
+): Promise<TestDebugPage> {
+  const client = { request } as unknown as GatewayBrowserClient;
+  const snapshot = {
+    phase: "connected",
+    client,
+    hello: { features: { methods: ["manual.first", "manual.latest"] } },
+  } as ApplicationGatewaySnapshot;
+  const gateway = {
+    snapshot,
+    eventLog: [],
+    subscribe: () => () => undefined,
+    subscribeEventLog: () => () => undefined,
+  } as unknown as ApplicationContext["gateway"];
+  const page = document.createElement("openclaw-debug-page") as TestDebugPage;
+  page.context = { basePath: "", gateway } as ApplicationContext;
+  document.body.append(page);
+  await vi.waitFor(() => expect(page.debugStatus).not.toBeNull());
+  await page.updateComplete;
+  return page;
+}
+
+function clickManualCall(page: TestDebugPage): void {
+  const button = [...page.querySelectorAll("button")].find(
+    (candidate) => candidate.textContent?.trim() === "Call",
+  );
+  if (!button) {
+    throw new Error("Expected the rendered manual RPC Call button");
+  }
+  button.click();
+}
+
+function diagnosticResponse(method: string): unknown {
+  switch (method) {
+    case "status":
+      return { version: "healthy" };
+    case "health":
+      return { ok: true };
+    case "models.list":
+      return { models: [] };
+    case "last-heartbeat":
+      return null;
+    default:
+      throw new Error(`Unexpected diagnostics method: ${method}`);
+  }
+}
 
 function createProps(overrides: Partial<DebugProps> = {}): DebugProps {
   return {
@@ -39,6 +110,7 @@ describe("renderDebug", () => {
   });
 
   afterEach(async () => {
+    document.body.replaceChildren();
     await i18n.setLocale("en");
     vi.unstubAllGlobals();
   });
@@ -95,4 +167,122 @@ describe("renderDebug", () => {
     expect(container.textContent).toContain("gateway");
     expect(container.textContent).not.toContain("Invalid Date");
   });
+
+  it.each([
+    { label: "response", staleError: false },
+    { label: "error", staleError: true },
+  ])(
+    "ignores an older manual RPC $label after the latest call succeeds",
+    async ({ staleError }) => {
+      const older = deferred<unknown>();
+      const latest = deferred<unknown>();
+      const request = vi.fn(async (method: string) => {
+        if (method === "manual.first") {
+          return older.promise;
+        }
+        if (method === "manual.latest") {
+          return latest.promise;
+        }
+        return diagnosticResponse(method);
+      });
+      const page = await mountDebugPage(request);
+
+      page.debugCallMethod = "manual.first";
+      await page.updateComplete;
+      clickManualCall(page);
+      page.debugCallMethod = "manual.latest";
+      await page.updateComplete;
+      clickManualCall(page);
+      await vi.waitFor(() => expect(request).toHaveBeenCalledWith("manual.latest", {}));
+
+      latest.resolve({ result: "latest response" });
+      await vi.waitFor(() => expect(page.textContent).toContain("latest response"));
+      if (staleError) {
+        older.reject(new Error("stale manual failure"));
+      } else {
+        older.resolve({ result: "stale response" });
+      }
+      await older.promise.catch(() => undefined);
+      await Promise.resolve();
+      await Promise.resolve();
+      await page.updateComplete;
+
+      expect(page.textContent).toContain("latest response");
+      expect(page.textContent).not.toContain("stale response");
+      expect(page.textContent).not.toContain("stale manual failure");
+      expect(page.debugCallError).toBeNull();
+    },
+  );
+
+  it("reports polling failures separately from manual RPC and clears them on recovery", async () => {
+    let diagnosticsUnavailable = false;
+    const request = vi.fn(async (method: string) => {
+      if (method === "manual.latest") {
+        return { result: "manual response" };
+      }
+      if (method === "status" && diagnosticsUnavailable) {
+        throw new Error("background snapshots unavailable");
+      }
+      return diagnosticResponse(method);
+    });
+    const page = await mountDebugPage(request);
+    page.debugCallMethod = "manual.latest";
+    await page.updateComplete;
+    clickManualCall(page);
+    await vi.waitFor(() => expect(page.textContent).toContain("manual response"));
+
+    diagnosticsUnavailable = true;
+    await page.loadDiagnostics();
+    await page.updateComplete;
+
+    expect(page.querySelector('[role="alert"]')?.textContent).toContain(
+      "background snapshots unavailable",
+    );
+    expect(page.textContent).not.toContain("Call failed");
+    expect(page.debugCallError).toBeNull();
+    expect(page.debugCallResult).toContain("manual response");
+
+    diagnosticsUnavailable = false;
+    await page.loadDiagnostics();
+    await page.updateComplete;
+
+    expect(page.querySelector('[role="alert"]')).toBeNull();
+    expect(page.textContent).toContain("manual response");
+  });
+
+  it("clears a failed snapshots alert when the Gateway source changes", async () => {
+    let diagnosticsUnavailable = false;
+    const initialRequest = vi.fn(async (method: string) => {
+      if (method === "status" && diagnosticsUnavailable) {
+        throw new Error("old Gateway snapshots unavailable");
+      }
+      return diagnosticResponse(method);
+    });
+    const page = await mountDebugPage(initialRequest);
+    diagnosticsUnavailable = true;
+    await page.loadDiagnostics();
+    await page.updateComplete;
+    expect(page.querySelector('[role="alert"]')?.textContent).toContain(
+      "old Gateway snapshots unavailable",
+    );
+
+    const nextStatus = deferred<unknown>();
+    const nextRequest = vi.fn(async (method: string) =>
+      method === "status" ? nextStatus.promise : diagnosticResponse(method),
+    );
+    const nextClient = { request: nextRequest } as unknown as GatewayBrowserClient;
+    const nextGateway = {
+      ...page.context.gateway,
+      snapshot: { ...page.context.gateway.snapshot, client: nextClient },
+      subscribe: () => () => undefined,
+      subscribeEventLog: () => () => undefined,
+    } as ApplicationContext["gateway"];
+    page.context = { basePath: "", gateway: nextGateway } as ApplicationContext;
+    page.requestUpdate();
+    await page.updateComplete;
+
+    expect(page.querySelector('[role="alert"]')).toBeNull();
+    nextStatus.resolve({ version: "replacement" });
+    await vi.waitFor(() => expect(page.debugStatus).toEqual({ version: "replacement" }));
+  });
 });