i have 2 games installed but only stellaris disappeared from gog Galaxy's library.
gog does not recognized that the game is there and yet glitches when you try to get to install or update.
the other game is just fine though.
In order to get stellaris working again i had to uninstall it completely. which worked the first time, but the second time uninstall did not completely remove the game, and had to delete the folder.