Glad it’s working for you.

I've just accidentally stumbled on some information in the forum that Avast has apparently caused problems with System Restore for some.

That’s not exactly what is presented in that other topic. They are talking about Avast, just because this is Avast Forum (and they want a better behaviour or workaround from Avast in relation to the issue). But the issue is present in many other security tools too.

In any case, that issue is completely unrelated to yours. In your case, the report was about password protected files, but the fact that they were in some restore point is almost a coincidence. The same type of report could had been received about some other files in some other folder, with no relation to restore points.