Nanite Foliage Assembly disappears when viewed from certain angles

I’m working on some very large douglas fir trees, and using the Nanite Assembly Pipeline. I’ve written an exporter that takes my trees from Blender into UE, with full instancing etc.

I am seeing that when the camera is close to the bottom or top of the tree, the tree will appear/disappear from view. Anyone know a fix for this? (Using Voxelization for shape preservation)