Good that you have found the true culprit.
Thanks for posting your update. Hopefully it will help others and save some grief.
Nice post - thank you.
I do hope it does help others who use Sandboxie.
Sandboxie is rather restrictive for updates and changes. Chrome or any other browser for instance cannot be updated within Sandboxie.You have to watch it and it can be easily overlooked when some updating or changes are made which then develop problems.
It seems and quite rightly so, that any program that has some external to browser component influence must be dealt with outside Sandboxie. I have hit this a few times, but it is so easy to forget Sandboxie`s behaviour. There is no general rule, some things can be updated within Sandboxie, it is illogical to the user, but not to Sandboxie.
Most Chrome extensions are totally confined to Chrome and updates or changes remain fixed. But Avast is an external program with an extension within Chrome. Therefore although changes remain OK within a session, they are disabled on browser closure, since they have not had permission to exit the sandbox.
I only thought of it as a last resort to my memory and previous experience.