Yes, those were normal windows, and not private or such. I looked around but there's no "recently closed" in "tab menu". Extremely rare.

Yes, in there I see it as tabs in different windows (or as separate groups), but there's no option to "restore last window closed" or such.

Is there something i can do to fix it? My opera version is 38.0.2220.41, i looked in the config's options but seen nothing. Again, many thanks for your time!

No, if i create new windows they're not listed in there. That button just shows me the tabs of the current window i'm.

Which is the "tab menu"? the arrow next to the plus sign or the page that appears when opening a blank tab? or what?
Thanks for taking the time to answer my friend.

I know i should explain more (according to the guide/rules), but i guess it's all said in the title... It would be great to have a way to recover a full tabed window when it's closed by accident. Or at least ask for a confirmation like "are you sure you want to close X tabs?" (when closing, not when quitting). I've been through this problem a lot of times, i accidently click on the close cross and can never recover what i had on that window. The only way i got to recover them is by going through the history log, but many sites in that window could have a few days so finding it again is a lot of work.

Hope you see this soon, and make something about it, would be a tiny but very helpful addition.
Thanks for the great work also!