Lots of pull: no available source device

A complete rescan doesn’t stop that output. How can I instruct syncthing to completely reset its internal status about the failed files?

I’m following the hint provided at Useful .stignore Patterns and have Thumbs.db in my .stglobalignore. syncthing, however, states that Thumbs.db is not synchronized. How can I instruct syncthing to really ignore that file?