Apps · App updates after a move
What does "Reinstalled by vendor" mean on a moved app?
Short answer: An updater installed a new copy on your built-in drive. Storage Studio flags it and moves the new version back to your fast drive once you quit the app.
It means the app's updater installed a new copy in the app's original place on your built-in drive. Storage Studio shows this on the Moved tab and sends a notification saying it will move the app to your fast drive again.
If the app is open, it waits until you quit it, then re-applies the move with the same safety checks. Nothing is lost — you just briefly had two copies.