thanks for youre response…
@ kenpimentel: i created the bug report as requested.
@pierre-felix: as you can see from my first pic/screenshot (bottom half) i have had turned on one render viewport already ( i always work with one on) and also saved during having it on. so that cant be the problem’s source i guess.
As the model looks fine in Rhino, but not in UE the problem should be in UE i guess. as even the dynamically lit model has errors, it may even be that is has nothing to do with the lightmap??? apart from the fact that UE creates wrong lightmaps as you can see for yourself if you import the fbx file and let UE do the lighmapping.