First point - you may be right about the bug affecting some systems, but your reasoning that otherwise the forum would be full is
suspect. I would guess the much more likely reason is that not too many users use system restore.

Why did I choose to use system restore ? Because of non-Avast related issues.

This problem is reasonably easy to reproduce. But look - we haven’t heard a single word from an official Avast representative.
I suspect they know what the problem is, but for reasons known only to themselves they will not divulge it.
It’s either due to a something in the registry, or the contents of a file. Notice it only ever switches from free > paid,
never the other way around.