Unfortunately the problem persists.
In this screen I had a queue of several media, and after one ended I got the modal dialog while the next started playing.
What do you mean in what process does it occur? How can I check that?
I also attempted to turn a watched but undeleted media as unwatched, then quickly skipped to the end, and replicated the issue again.
But this time the watched video kept its watched status only while the empty modal dialog was on, then it reverted to unwatched state.
This is the video before it was watched (skimmed quickly to the end)
Then after skimming the video gets watched flag, and an empty modal dialog
Then another modal dialog shows up that tries to set the watch count, and the video loses its watched status, reverting to unwatched