FPS drops upon hitting trees/nodes?

Had a few players complain that when they hit a rock or tree on my server that their framerate drops considerably. I tested myself and mine does drop but it's not enough to be noticable. Could this just be solely based on their own machines or is there possibly something i can do to help this to help them?

Plugins i think may be associated
ZLevels
Rewards
Stacksize controller


I feel like it's just a mix between their machine and the game just not very well optimized. But what bothers me is that they say it only happens on my server.

 

It happens on my server too.

 

Then maybe it's just a game optimization issue