Not sure but IIRC there is an issue with foliage and landscape grass tool in which the instances won’t have any LOD’s. Recently Epic did some internal changes to LOD’s so if you move an old asset from an older engine to 4.16, the LOD’s wont transfer. That means even distance meshes in foliage/grass tool will still load LOD0 which causes the FPS drop. This is what I think is the issue is but let’s wait for an Epic staff to chime in. 