@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 ?
Probably due to a microphone access crash. If that's the case for you note that regular Opera has a fix for this issue. See DNA-107508 at https://blogs.opera.com/desktop/changelog-for-98/. Opera GX just hasn't gotten the fix, but will soon.