Why does a watched video become unwatched over time?

Question

YouTube

The issue is that recently watched videos are not marked as unwatched, even those on which there are likes.
I identify a video by the red bar below the video.
Is it possible to disable or make it so that watched videos are not deleted as viewed.

Guessing - 1 optimizing views but then there should be a feature to turn it off. I visited the site - https://myactivity.google.com/activitycontrols/youtube But it is automatically there

Data is saved - YouTube history is enabled
Automatic deletion (disabled)
These are my settings on the site.

2 that this site is not responsible for the red stripe. But if it was considered that after 3 months what was viewed disappear, then 3 more months have not passed for me. Why 3 months? Because this is the shortest period for deleting watched videos beyond 18 and 36 months.

First viewed videos - 31 August.
Reason for creation - As I thought before that this is a bug of the account, so I decided to create a new one. But now it disappears in this account too

Answer 1

Youtube algorithms are amazing! You are not the only one with this problem. It seems to me that it will not work to solve it with a click. most likely it is a bug of servers\code\client\yutuba site.