In UE4, the vegetation tool is used, and the shadow problem occurs only when the model is far away from the camera. Displaced objects will also have shadow problems, and they are not friendly to ray-traced shadows.
In UE5, this problem is magnified! ! ! There are such problems on nanite.
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Same issue - 
I have enable ray traced shadows both directional and skylight and nanited mesh (in front) is generally worse
Not sure if this is updated since the early access 2, but when you convert static meshes to nanites with raytracing you want to make sure the proxy triangle percent is 100% to the base mesh, so nanites and RT are getting the full detailed mesh to work from.
In the static mesh details under nanites
i don’t have Proxy Triangles option (UE5 Preview 1) so im assuming its named differently or something but only way i could fix nanite shadows was to change “fallback relative error” to 0
All raytracing features and Lumen in Hardware Mode are using the the fallback mesh and thats problematic. You can set your “fallback relative error” to zero for a highpoly fallback mesh but I’m pretty sure that this will have a huge performance impact. Not even sure if that sort of makes nanite useless?
In UE 5.2.1, you can execute r.RayTracing.Nanite.Mode 1 in editor console to fix raytracing shadow.
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You are a saint…