Hi @Dor,
Thank you for reaching out to Microsoft Q&A. We're happy to support you with your concern.
From our test results in the Teams web version in Edge browser, the hide chat feature is working as expected: when I hide a chat, it won't reappear until there's a new message or I unhide it.
However, we want to inform you that there's currently another issue with Teams channel view and combined chat.
Microsoft has already acknowledged this issue and our backend engineers is current working to resolve the issue. In the developing process, there may be some unexpected behavior happen, and I suspect your issue may be due to this situation.
We strongly recommend you submitting your feedback about your situation via the Microsoft Feedback Portal or directly through any Microsoft 365 app by going to Help > Feedback or File > Feedback. We will also inform Microsoft about this issue so they will also aware and optimize the hide feature as well as the current active issues to provide the best experience for our customers when using Teams.
Thank you for your contribution and understanding. If there's anything else I can help you with, please feel free to reach out again.
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