Media watch status no longer persists on media rename. When you move or rename your media files, previously Jellyfin remembered the watch status based on external IDs alone; now it uses an actual reference to the database entry. This is a transitional change and we are working on a better way to handle that in a future version.
I hope they do figure out a solution for that soon... Until that's fixed I'm going to stay on 10.10.7 for a while.