Short answer:
Disable Flush Grass Streaming and Flush Streaming Managers in Movie Render Queue → Game Overrides
Long answer:
I was having this issue rendering an outdoor environment that used the grass system for procedurally generating trees and grass.
ScatterBufferSize was the 1st clue…
I first disabled the grass entirely in my scene since it is “scattered”, then the render worked.
So at least the source of the problem was targeted.
Then, I was able to poke around Movie Render Queue to find a setting that controls the grass streaming.
Movie Render Queue → (+) Setting Dropdown → Game Overrides → Rendering Rollout:
Untick Flush Grass Streaming
Untick Flush Streaming Managers
This will cause the grass system to stream instead of create them all at once in a buffer…so you may need to adjust your animation to give all of your grass instances time to load.
Btw, this doesn’t have to be grass, it could be any instanced foliage / meshes that are spawned using the grass system.