GOG troubleshooting - JosefNemec/PlayniteExtensions GitHub Wiki

Some games appearing as uninstalled in Playnite

Playnite can report some games as "uninstalled" even if they appear installed in Galaxy client. This usually occurs if you import games to Galaxy via "Scan and import folders" feature instead of installing games fresh. Repairing game installations in Galaxy fixes the issue.

Some uninstalled games don't import

Make sure those games are not hidden on your account. You can check here by searching for those specific games and showing hidden results.