But you know, in a review made by Digital Foundry, they found out Horizon: Zero Dawn (PS4) doesn't have physics applied to grass or a lot of environment objects when the character goes through them. Here, the grass has to realistically move to the passing of Link and also the wind. Also, the physics are handled by the CPU, which has a constant speed regardless of the mode the system is running at in order not to interrupt game logic like, you know, the grass, heh. I'm betting that's what's causing the drops, having to apply physics on the grass (and other objects on the environment).

In any case, yeah, hopefully they'll improve it a bit with future patches.