I have, but I wish I could explain exactly what’s happening to you and I currently cannot.
You can see the same issue in the matrix demo with some thin geo, it does get crushed. What’s strange is that it seems the way the mesh is constructed affects whether or not it does get crushed.
For example, UE4’s default bush asset. Alpha-masked geometry, I placed well over a million of them and there was no perceptible loss of detail, as well as for a few different trees, small plants, etc. But other assets, different pieces of foliage did suffer from visual crunch. It’s almost like the specific way the geometry is carded is affecting the behavior, but I’d need to do more work.
Disclaimer: The nanite pipeline was updated recently and I haven’t been able to test it yet, so there is a chance the problem was solved. But essentially, some nanite foliage will work excellently, and others will break the pipeline. Depending on the scope of your work you may be able to experiment with it, but I can also totally understand not making the switch at the moment. I’ll let you know what my results are, because there is a chance Nanite foliage may now just work.