My posts get de-indexed

Some of the already indexed posts get de-indexed, this happens not the first time.
After I index them again manually, they get indexed again, but time later I find other posts de-indexed...

Currently de-indexed posts:
https://pueblacity.com/main-theater/
https://pueblacity.com/child-friendly-tourist-attractions-in-puebla-mexico/
https://pueblacity.com/environment-flora-and-fauna/
https://pueblacity.com/tourist-attractions-in-puebla/
https://pueblacity.com/5-de-mayo-facts-meaning-and-celebrations/
A few months ago, these posts were indexed, but some other ones were not indexed, so I added them manually, and finally, all posts were indexed.
Now I see these 5 posts are non-indexed.
I am sure if I will index them manually, they will get indexed again.
But I am also sure, that a few months or weeks later, I will find other non-indexed posts that now are indexed.
I have the same problem with all my sites.
There is no detailed explication, GSC only says "Actually not indexed".