@leocg To solve this problem I simple delete the file "Preferences" that are located in different places depending if in Linux or Windows (I don't have a Mac).
The issue is that for me I need to reinstall the addons, but the bookmark and history are preserved.
So in my GNU/Linux installed system the file preferences stay in a path like:
In Windows installed system the path is:
C:/Users/username/AppData/Roaming/Opera Software/Opera Stable
Yes, I tried the same workaround time ago and it worked.
Additionally, I found also that enabling sync on another pc with the same build (my laptop) was returning the problem.
Now I'm without Opera on that laptop...