Thanks Pupi, I also find it strange, but apparently this is what is happening.
I did some testing.
I accessed multiples accounts, old and new. With high and low scores. Administrators or not.
Pages load at least 3 times faster with accounts with more points. Pages load fast for visitors too.
I thought the problem was with the latest accounts. But I accessed one of the first accounts of the site that had no publications yet and was also quite slow.
I also removed almost all points from an account at the beginning of the site that has several publications.
And it kept running normally, the pages load fast.
I made a change in the core recently:
But, the problem continues even when the user reaches enough points to be able to send private messages.
(I have removed this change. The problem continues. It is not the cause of the problem. I added it again.)
I made few other changes in the core. I believe that no other can be related (hide administrator profile privileges, disable downvotes and disable use of emoji).
For the rest, my site is fully version 1.7.
The theme is an adaptation of 1.7.1, changing colors and sizes.
I also use moderation on the site for users with less than 305 points.
Only users with more than 305 points can post in wall.
Only users with 1,000 + points can upvote and flag.
My plugins: Core Plugins + Q2A embed, Facebook like box, Faq Page, Featured questions, My followers page, on site notifications, Next previous questions and Widget Anywhere.