New Hooks Are Suddenly Not Working Anymore

Your code here:
https://ibb.co/zQwrSgy

is not the same as my code:
https://generatepress.com/forums/topic/news-hooks-are-suddenly-not-working-anymore/#post-1865469

Can you please copy and paste my code?

Sorry about that. I missed the part that you flipped the condition. I fixed it.

Now it shows 7 on the first page, 8 on the remaining pages which are correct. However, one post between page 1 and page 2 went missing. I see test9 and test7, but test8 is gone.

Does that happen with just my code added?

If so unfortunately I'm out of ideas here - you might need to check with WordPress support team on this.

The same issue should appear if you use a default 2021 theme with the same filter. The pre_get_post is a WordPress filter unrelated to the theme.

No problem. Thank you for all the support. :)

No problem :)