While standing near a lot of tall grass in, the FPS drops from 60 to around 40 I'd say, it gets really bad. FPS drops only when near Tall Grass, this issue has happens to other people as well. (And my pc rig isn't bad.)
Steps to Reproduce
Go to the Wild Plains biome and stay near a lot of Tall Grass.
This issue has not been confirmed by a developer yet.