Nanite doesn’t cull assets, for foliage this is terrible because it will cause a huge amount of overdraw since you’re always drawing LOD0 while keeping the same need for the engine to render through so many transparent layers.
Best way to fix this is to change the way you think when making foliage for nanite. Triangles are not really a problem anymore, so you need to model any foliage as close as possible to the opacity map to minimize transparent areas, then in the shader you need to fill the opacity based on distance to the asset, in practice removing opacity after x distance. If you did a good job making geometry that has similar silhoutte to the opacity map and have good padding on your texture you shouldn’t notice too much visual difference.
If you use VSM and the foliage has WPO enabled you will also destroy performance. Ideally we would be able to have a static shadowcasting mesh so VSM can cache the shadows but don’t think this is possible with anything but maybe static meshes you placed by hand, not foliage.