dotnet/aspnetcore · error · Error

Invalid sequence number or identifier

Error message

Invalid sequence number or identifier '${sequenceOrIdentifier}'.

What it means

`resolveElement` maps a `sequenceOrIdentifier` (sent by the server when attaching a root component) to a logical element. It first checks JS-added pending containers, then tries to parse it as a numeric sequence for a .NET-added root component. If neither lookup succeeds the identifier is unresolvable, so it throws to prevent attaching a component to nothing.

Solutions

1. Ensure client and server share the same Blazor build so root-component descriptors/sequences agree.
2. When adding root components from JS, register the container (`addRootComponent`) before the server-side attach can fire, and avoid removing it prematurely.
3. Review the order of `UpdateRootComponents`/`AddRootComponent` operations to confirm the identifier is valid at attach time.
4. Capture the offending identifier from the message and correlate with server-side root component registration logs.

// before attaching, confirm the identifier is resolvable
function canResolve(seq: string, mgr: RootComponentManager<any>): boolean {
  return getAndRemovePendingRootComponentContainer(seq) !== undefined
    || !Number.isNaN(Number.parseInt(seq));
}

try { return cm.resolveElement(sequenceOrIdentifier); }
catch (e) { if (/Invalid sequence/.test(e.message)) { /* drop the attach op, log */ return null; } throw e; }

When it happens

Trigger: The server sends a root-component attach message whose `sequenceOrIdentifier` is neither a pending JS-added container key nor a parseable numeric sequence that `RootComponentManager.resolveRootComponent` can resolve.

Common situations: Mismatched client/server versions where the server registers a root component descriptor the client doesn't have; JS-added root components whose container was already consumed/removed before the attach message arrived; desync in root-component registration during hot reload or render-mode changes; corrupted/out-of-order add-root-component operations.

Related errors

• The circuit associated with this dispatcher is no longer…
• Cannot start a disposed circuit.
• Cannot start the circuit until Blazor Server has started.
• Circuit host not initialized.
• Circuit state is already in progress

AI-assisted analysis of dotnet/aspnetcore@3600ca084e (2026-08-11). Data as JSON: /api/errors/43ab4411e957377c. Report an issue: GitHub.

Appendix: source

Thrown at src/Components/Web.JS/src/Platform/Circuits/CircuitManager.ts:559

    this.changeActivity(1);
    return sendJSDataStream(this._connection!, data, streamId, chunkSize, () => this.changeActivity(-1));
  }

  public resolveElement(sequenceOrIdentifier: string): LogicalElement {
    // It may be a root component added by JS
    const jsAddedComponentContainer = getAndRemovePendingRootComponentContainer(sequenceOrIdentifier);
    if (jsAddedComponentContainer) {
      return toLogicalElement(jsAddedComponentContainer, true);
    }

    // ... or it may be a root component added by .NET
    const parsedSequence = Number.parseInt(sequenceOrIdentifier);
    if (!Number.isNaN(parsedSequence)) {
      const descriptor = this._componentManager.resolveRootComponent(parsedSequence);
      return toLogicalRootCommentElement(descriptor);
    }

    throw new Error(`Invalid sequence number or identifier '${sequenceOrIdentifier}'.`);
  }

  public getRootComponentManager(): RootComponentManager<ServerComponentDescriptor> {
    return this._componentManager;
  }

  public getEventRegistry(): JSEventRegistry {
    return this._eventRegistry;
  }

  private unhandledError(err: Error): void {
    this._logger.log(LogLevel.Error, err);

    // Disconnect on errors.
    // Trying to call methods on the connection after its been closed will throw.
    this.disconnect();
  }

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