Hello! My name is Nazia, and I am an Independent Advisor as well as Microsoft user like you. I will try my best to help you with an appropriate answer .
I am sorry to hear that you've experienced this, it sounds like this channel is created by that user as private and that is why the task is not being assigned other user. There are certain limitations in a private channel and it is not possible to convert a private channel to another channel type.
Regards,
Nazia
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