VF ending chat on certain specific questions

I have a chatbot that is integrated with an openai assistant. For many questions, it works fine, as expected. But a very weird thing seems to be going on which is that certain questions just end the chat. User gets you have ended this chat message it just ends.

Hard to detect a pattern, but one thing we are observing is that the more directly the questions are related to the KB (which we have in the openai assistant, not on VF platform), the more likely the thread just ends.

Has anyone seen this or have any suggestions on how to find the gremlin? There's nothing obvious in debugging.

Thanks!