Why is my foliage disappearing?

Hey guys I have been trying so desperately to get my foliage to render as you would expect it to. Both in the viewport and my render, the foliage disappears/reappears in multiple levels I have. It doesn’t matter if your far or close, it just flickers. I am doing cinematic renderings in 5.1, so performance doesn’t matter.

Here you can see the foliage properly rendering

But a few frames later it has disappeared

Then in this scene, the foliage looks fine in the viewport

But only the shadows appear in the render.

Some help would be much appreciated, as this is driving me crazy!!