When your self-hosted Alby Hub stops working, the first thing you should do is reset your node and reenter your Alby credentials. That fixes most failures. Interestingly, this doesn't happen with nodes hosted on Alby Cloud, only self-hosted nodes (Start9, Umbrel, etc.)
Discussion
Sounds pretty cluegy that's necessary...
I think it has something to do with the communication link between the node and Alby Hub. For whatever reason, the connection is temporarily interrupted, and Alby is unable to automatically recover. That's what I suspect after seeing this problem several times.