I had to modify game.project
and errors went away. Only after 1.9.5 update did I need this, though.

Jay_Cee:
Too bad for me it comes in the shape of WARNING.GAMESYS ‘Material’ issues
In your custom materials? Or the built-in materials?
In my custom materials. I made a back up, clean the files, then the engine kept crashing, so I return back to the old state to keep working.

Jay_Cee:
Also, in Windows 10, Ctrl+/ for code comments n longer works
Do you have any custom key bindings or are you using only the defaults?
I do have a custom key binding file. Worked up until 1.9.5.
Note: I switched from 1.9.1 → 1.9.5. None in between.