A common problem I’ve come across recently with Game Pass is that none of my installed games will appear in the list to the left of the screen (only Microsoft Solitaire Collection will be displayed which was installed by default). As a test I installed another game to my C: drive, this remained when all other titles disappeared so it seems games installed to the boot drive/default install location are unaffected.
A simple restart of the Xbox application will make installed games reappear usually. I’m yet to determine the exact cause, so, unfortunately, do not yet have a permanent solution. I’ll update this article when I figure out more as at the moment this issue occurs at least once per day on my primary PC.