cPFence
I also encountered some issues when upgrading to v12.
But luckily they released updates very quickly. So far there have been 17 updates.
The most critical thing I see is backups.
But it looks like an update is already in the works to fix the backups issue.
The problem I had with the license being "disconnected", leaving the panel unusable, I also reported to Adam.
This happened after I ran the last update, although I don't know if it's related.
I suspected it because all 26 connected servers were having the same problem.