Ok, now I got at least a crash message on 4.11 P4:
Assertion failed: AttachedActor->ParentComponent->GetOwner() == this [File:D:\BuildFarm\buildmachine_++UE4+Release-4.11\Engine\Source\Runtime\Engine\Private\ActorConstruction.cpp] [Line: 283]
Interesting note: When I set startup map to an empty testmap, everything works ok. It STILL works ok if I place my BP_Car_Bentley in map (very complex, various child actors). I can also start a PIE session without a problem.
But as soon as I save map, it crashes on next startup.
Deactivating construction script of BP_Car_Bentley completely doesn’t change that.
So it seems a problem of level loading, neither than asset itself (which worked in all previous engine versions).