I was able to repro this issue in Vanilla UE. So basically I setup a humanoid (6 LOD generated) mesh in the empty map and SetForceLOD(1), have a trigger cube to hide the mesh or unhide when out. And then set r.Streaming.Poolsize 1 (I have to super aggressive on this cause there only 1 mesh in the mesh)
Try to walk in&out the hidden cube and oberse mesh I can see the mesh pop.