Echo cancellation doesn't seem to always work - how to troubleshoot?

### Your use case

I would like to troubleshoot the case, when echo cancellation doesn't seem to always work. I have a case when I speak with one person and he hears the echo, unless uses a headphones.

That is currently the only one person and I wonder how to troubleshoot that

### Have you considered any alternatives?

Yep - I've checked the code and have found that echo cancellation is enabled.

### Additional context

_No response_

The issue names no files or tests; start by reproducing the one-person call with and without headphones, then inspect the TypeScript code where echo cancellation is enabled. Done would mean identifying why cancellation fails for this case and documenting or fixing the confirmed cause.

Written by the indexing model from the issue text.