Just double check your nanite scene to see if there are any fallback mesh shenanigans, but also try these cvars:
r.RayTracing.Culling.PerInstance 0
r.Nanite.MaxPixelsPerEdge 0.5
r.nanite.maxnodes (try changing this to a higher value than it’s currently set to)
Found those last two in Nanite foliage disappearing when camera moves away - #3 by Origenic - goes in to a bit of an explanation. I found those helped quite a bit.