Nextcloud Talk App Android - Chats are invisible

Hello there,
i am facing in issue with some Users in my Cloud using NC Talk on Android devices. When I login to their Accounts on a mobile device (tested only on Android) I no longer see the Chats. The only thing I see are grey bars. Is it possible that some users are blocked by NC to use the talk App on a Android Smartphone and if so how can the user get unblocked?
Is there anyone who had the same problem before?

Thank you!

Problem is solved.
The device could not load the chats because there were too many open chats at the same time.
Data overload?!