I think something is wrong with that rock at zone 738 - 658/788/516

Whenever I look at it, my FPS goes down from 60 to exactly 30 - not more and not less, until I look away again.
I tried looking at the rock from all directions and it's all the same.

Anyone else is having this issue? Could it be a memory leak, or so?

EDIT:
More rocks which cause this:
739-870/875
780-855/689