dotnet/aspnetcore · critical · Error

Circuit host not initialized.

Error message

Circuit host not initialized.

What it means

Thrown inside the SignalR 'JS.SavePersistedState' handler when the server sends persisted component/application state before _circuitId has been assigned. _circuitId is set only after a successful StartCircuit invoke, so receiving SavePersistedState before that point means the circuit handshake ran out of order or against an uninitialized circuit.

Source

Thrown at src/Components/Web.JS/src/Platform/Circuits/CircuitManager.ts:166

    connection.on('JS.AttachComponent', (componentId, selector) => attachRootComponentToLogicalElement(WebRendererId.Server, this.resolveElement(selector), componentId, false));
    connection.on('JS.BeginInvokeJS', (asyncHandle: number, ...rest: unknown[]) => {
      if (asyncHandle !== 0) {
        this.changeActivity(1);
      }
      (this._dispatcher.beginInvokeJSFromDotNet as (...a: unknown[]) => unknown)
        .call(this._dispatcher, asyncHandle, ...rest);
    });
    connection.on('JS.EndInvokeDotNet', (asyncCallId: string, success: boolean, resultJsonOrExceptionMessage: string) => {
      if (asyncCallId) {
        this.changeActivity(-1);
      }
      this._dispatcher.endInvokeDotNetFromJS(asyncCallId, success, resultJsonOrExceptionMessage);
    });
    connection.on('JS.ReceiveByteArray', this._dispatcher.receiveByteArray.bind(this._dispatcher));

    connection.on('JS.SavePersistedState', (circuitId: string, components: string, applicationState: string) => {
      if (!this._circuitId) {
        throw new Error('Circuit host not initialized.');
      }
      if (circuitId !== this._circuitId) {
        throw new Error(`Received persisted state for circuit ID '${circuitId}', but the current circuit ID is '${this._circuitId}'.`);
      }
      this._persistedCircuitState = { components, applicationState };
      return true;
    });

    connection.on('JS.BeginTransmitStream', (streamId: number) => {
      const readableStream = new ReadableStream({
        start: (controller) => {
          this.changeActivity(1);
          connection.stream('SendDotNetStreamToJS', streamId).subscribe({
            next: (chunk: Uint8Array) => controller.enqueue(chunk),
            complete: () => { controller.close(); this.changeActivity(-1); },
            error: (err) => { controller.error(err); this.changeActivity(-1); },
          });
        },

View on GitHub (pinned to 294cab2f9b)

Solutions

1. Ensure the blazor.web.js / blazor.server.js version exactly matches the ASP.NET Core server version shipping the app.
2. Let the framework own circuit lifecycle; do not manually pause/resume or send state out of band.
3. On persistent errors, force a full page reload to re-establish a clean circuit handshake.

When it happens

Trigger: Server-initiated persisted-state push arriving during/after a connection race, a reconnect/restart sequence where the prior circuit was not fully established, or a server version mismatch sending SavePersistedState earlier than the client expects.

Common situations: Circuit resumption (pause/resume) flows under poor connectivity; running a newer server against an older blazor.*.js (or vice versa); custom reconnection handlers that interfere with circuit startup ordering.

Related errors

• Received persisted state for circuit ID '${circuitId}', but
• Blazor Server has already started.
• Cannot start the circuit until Blazor Server has started.
• Cannot start a disposed circuit.
• Circuit options have already been configured.

AI-assisted analysis of dotnet/aspnetcore@294cab2f9b (2026-08-06). Data as JSON: /api/errors/4fa762bf46f52514. Report an issue: GitHub.