@eugenialoli @jbqueru I see. You mean "anonymous" session, without explicitly saving one. I never noticed that since I never needed it. Probably best to file a wishlist report about this at
https://bugs.kde.org/enter_bug.cgi?product=kate&bug_severity=wishlist
If it is not already in the system. Or if maybe somebody else knows if it is possible to enable that. I remember seeing it work with X11 session restore long time ago when I left Kate running and restarted the computer and it restored even unsaved files.