Hello. I strongly recommend High priority, despite it is not page content lost, but still, the user loses a lot of information.
- User A has page X in their watchlist.
- There are a couple (one is enough, but let's say 5) unseen revisions of X.
- Before revision 1 there was their own revision of X.
- User C thanks to user A for that revision.
- User A gets notification about this thank.
- User A clicks on notification and opens the thanked revision.
- Unexpected result: Revisions 1-5 marked as seen.
Recognized many times, including five minutes ago. But at least once it worked as expected.