Additional meeting and call-related features and issues within Microsoft Teams for business
Hi Patrick,
My name is Didi. I'm happy to help you today.
Sorry to hear about this issue. Could you try clicking on the ellipsis (...) at the right of the team name > Manage team > Channels?
Then, try finding the missing channel from the list, check to show for members, and see if there's any difference.
Have you also tried using the web app, https://teams.microsoft.com/, to check if the channel appears from there?
Best regards,