Maybe you missed something that was posted. Your first suspicion is that Avast is behaving differently. Maybe.

But maybe some other software is now behaving differently (Adobe password - protecting files) and that’s the reason. System Restore would be building the backups from the same files tahn before, but now those files are password protected, and Avast can’t do anything about it.

This is one possibility, already mentioned above. I’m just expanding the explanation.