I noticed this morning, a lot of posts in some topics disapeared when logging in ...
There where 7 pages of posts in the "This place just doesn't die" thread before logging in and only 4 afrer I logged in

Maybe some bug ?

No, likely you have the number of posts per page set differently than the default setting. I have mine set so that I have no pages, every post is on one massively long page. I believe the default is 10 posts per page, but you can change it to 10, 25, 35, 50, 75, 100, or unlimited (which is what mine is set to).

Gentlemen,

There is a secret moderator among us.

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@jmasterx: As Specter pointed out above, you can set how many posts per page in the control center, and apparently your personal setting is different from the default setting for anonymous visitors, so you can see more posts per page resulting in fewer pages, although the total amount of posts is the same.

I know I was just teasing

I intentionally set those settings years ago.