I think at some point I mustve accidentally set in the World Settings → Game Mode Override, my C++ GameMode Class. It seems once this was set, it didnt matter what was in Project Settings.
Now I changed World Settings → Game Mode Override to None, and now Project Settings works again. What I choose now as default in Project Settings will be used.
As to when / why I had put the World Settings → Game Mode Override to C++ Class I do not know. Probably at the start of the project I looked at World Settings and maybe there I set it accidenttaly.
But thank you for replies! As a plus you showed me a cleaner version of my spawning code 