Holy hell thank you so much for this. This is the third time I encountered this problem and I stumbled upon this finally figuring out the problem as I also use Webroot. No wonder why this keeps messing up. If you're reading this you're a godsend you saved me from wiping my computer clean for a 2nd time. Also Opera and/or Webroot should really crack down on this problem and fix what's causing it instead of ignoring it and causing others like me to think that restarting their pc is the only way to fix it.
@leocg So, in username\AppData\Roaming\Opera Software\Opera GX Stable\Sessions then, right ? Considering that said folder only contains a single session file, I guess there is no other way to recover it ?