No Idea. However i suggest checking out packaged build files.
Download software named: “UE Viewer”
Try opening your packaged build and see if game mode is packaged in game files.
Also if you don’t want to use “UE Viewer” i think there is option to package all game files seperately, not in big .pak files? I’m not sure about this, but you maybe it helps you to see if game mode is in packaged build or not.
If game mode is in files… then something else is wrong. Log files don’t write any useful info about it, right? Maybe someone else will be able to help.