"This ensure is intended to catch regressions where rendering programmers add a loose parameter to LocalVertexFactory, breaking dynamic instancing on regular static meshes. InstancedStaticMeshes cannot be dynamically instanced so the warning should not be triggering for them. Somehow we need the VF to communicate to this renderer code whether it expects to be dynamic instancing compatible or not, so we can implement the ensure properly. Something like SupportsCachingMeshDrawCommands(), which is already checked. Perhaps this is fixed in latest."
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-79770 in the post.