Intermittent failure of VizQL startSession/viewing when using Embedding API v3 in Angular SPA

We are embedding Tableau dashboards using Embedding API v3 (<tableau-viz>) inside an Angular SPA.

While embedding, we consistently observe that one internal VizQL request:

/vizql/.../startSession/viewing

intermittently fails with a “Page unavailable / content doesn’t exist” response in the browser network tab. However:

• The dashboard still loads and renders successfully
• Other VizQL requests execute correctly
• The issue does not impact user functionality
• This occurs mainly in an SPA context (Angular route navigation / component lifecycle)

We understand that VizQL endpoints are internal and not part of the supported public API surface, and that Tableau manages session handling internally when using Embedding API v3.

Our questions:

1. Is it expected behavior for startSession/viewing to intermittently fail while the viz still renders successfully when using Embedding API v3?
2. Can this failure be safely ignored if the dashboard loads and firstinteractive fires?
3. Are there any recommended best practices for SPA frameworks (Angular) to avoid duplicate or racing VizQL session initialization?
4. Is there any official documentation confirming that such VizQL failures are non-blocking in embedded scenarios?

We want to confirm that this behavior is by design and that no application-side changes are required, as long as:

• The workbook/view exists and is not renamed or deleted
• The embed URL is correct
• Proper permissions/access are maintained

Any clarification from Tableau would be appreciated.