There is an odd issue when converting a landscape that has LGT spawning on it to Nanite, where the grass density seems to break.
As you can see in the images enabling Nanite gives it some kind of stroke like pattern where a lot of grass is missing in areas they were not before.
Nanite
Old
Already tried most of the obvious stuff like flushing the grass cache, rebuilding grass maps, rebuilding the Nanite landscape but no luck