Videos can't have "watched" status and/or "Remove watched" doesn't work and/or "playback position" feature is bugged

[Tallefer]

Checklist

• I am using the latest version - 0.21.14
• I checked, but didn't find any duplicates (open OR closed) of this issue in the repo.
• I have read the contribution guidelines given at https://github.com/TeamNewPipe/NewPipe/blob/HEAD/.github/CONTRIBUTING.md.
• This issue contains only one bug (HOPEFULLY). I will open one issue for every bug report I want to file.

Steps to reproduce the bug

1. Make a playlist and add videos to it
2. Play one or more of those videos till the end or/and use "Mark as watched" from video's context (long tap) menu
3. A red progress bar under each watched video should be visible now (it is not immediately visible in the "What's new" tab so either go to the playlist or press "Refresh", not sure if it isn't another bug)
4. In the playlist view press "Remove watched', then "Yes".

Actual behavior

• No videos are removed.
• The red progress bar often (not always) misses a chunk from its end, most noticeable on short (3-5 min or less) videos.

Expected behavior

• All completely watched videos should be removed.
• All completely watched videos should have a full red bar under them.

Just a wild guess - bug could be related to how preloading next video while still playing the current one is implemented, based on those incomplete red bars.

Screenshots/Screen recordings

Logs

Device info

• Android version/Custom ROM version: 5.1.1
• Device model: SM-J120F

[Tallefer]

This bug is present for at least 6 months, probably more, but the removal feature worked just fine for some time since its introduction.

[LingYinTianMeng]

I want to work on this issue， I am working on it and I think I can fix it soon

[LingYinTianMeng]

I guess the original code just forgot to take into account the condition if the video is finished, I'll try to add it

[LingYinTianMeng]

I think I've fixed it, can you assign it to me?