Unable to receive messages from a particular set of users and mobile app "accept" can't be clicked

[ddonep74]

I had an issue whereby I wasn't receiving replies from a few of my team members on Teams. It turned out that somehow they were blocked, despite me never having blocked them (there isn't even a block button anywhere on our Teams Windows app). I unblocked those users and then I was able to receive messages from them again (although I did also lose all conversation history from half of them - it turned out that there were 8 people magically blocked not just the members of my Team). 

Now today, I'm unable to receive messages from them again and my blocked list is definitely empty:

However, if I look on the mobile app, I see this:

If I click "Accept" nothing happens. All these users are in the same domain/AD, so there's no reason they'd need permission to chat anyway.

Now, if I click "Block", then the user appears in the block list. If I then unblock them, I receive messages again. So it appears like all these users have become magically blocked again, despite not appearing in the block list.

I've tried clearing all app caches on both Windows and Teams, I've tried uninstalling and reinstalling everything, etc. Our IT department is unable to see anything wrong from their end.

[#2]

@ddonep74 

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