I have installed MW5 on an SSD and today I noticed, that it's not listed as installed. I haven't played the game for some time, so I thought, that after my last system wipe, I might have not installed it again, so I pressed install. Nothing happened. So I checked and saw, that it's already installed on the SSD. I tried the "scan folder" option. Nothing. Downloading the files for off line use. No, no reaction. Tried to install it on a different HDD. No, doesn't work. Anyone any idea?

Assume you've attempted the "add games manually" or "scan folders for games" options with GOG Galaxy?