@erik1000 You are not alone!
I have had this happen a couple of times as well, where ropening Opera did not load the previous session and I was unable to retrieve my session.
I currently make ‘snapshots’ of all my tabs twice daily by right-clicking any tab and selecting “Save All Tabs as Speed Dial Folder”. This ensures that I have a backup of the tabs I am still meaning to read but have ‘aged’ in my History, making it a nightmare to recover (if I am still able to remember part of the page name or URL), while still allowing the tabs that are unrecoverable be in today’s History.
This, together with the Close Tab shortcut functionality randomly closing the whole window (https://forums.opera.com/topic/29322/cmd-w-closes-the-window-instead-of-the-tab/2) makes Opera more and more a nightmare to use as main browser…