At this point I'm not leaving useful tabs open on Opera anymore, but it is still annoying when this happens.
If I open Opera on incognito (with no other Opera windows active), and it happens to load that incredible annoying window with sound (Genius idea, btw. You should try adding something like the old SWF autoplay videos on loop of the old days. People would surely love them too!), that I guess happens when Opera gets an update, all my tabs on my normal session are lost.
So, in short:
I open Opera in incognito.
That annoying thing pops out.
I close the incognito window.
I open a normal Opera session.
It opens with only a new tab open. All my previous ones lost.
At this point I'm not even interested on geting them back. But dude, how can this still keep happening? I posted about this same issue months ago.
Windows 10 and latest Opera version to this date.