Me and a friend build a map of sth in a Desert and to have some variation we added suspicious sand to it, alot of it which caused a severe lag drop.
It was in a flat world and I normally have around 180-200 FPS with shaders on, which then dropped down to less than 60 FPS with just having suspicious sand in it.
You can reproduce it by placing alot of that sand on one spot.

idk the mc commands for that, I used WorldEdit