Adjacency buffer needs to be enabled in the static mesh build settings. It's not enabled by default if the imported materials don't require it.
Meshes imported from rhino are not compatible with 'Crack Free Displacement'
Result: Materials with Crack Free Displacement enabled will show only default grid material on meshes imported from Rhino
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-84946 in the post.