Hey ,
The actor is spawned from C++ with GetWorld()->SpawnActor. The spawn code is executed from a delegate that is tied to the UPrimitiveComponent::OnComponentHit.
As for reproduction steps, I will see if I can setup a fairly empty scene to reproduce the issue. Keep in mind that we have not been able to reproduce the issue on yet, only on consoles. With different reproduction rates between the consoles. But looking at the code it does appear to be a generic issue.
Here are the callstacks of the threads which are in the deadlock:
(Red is where the render resources are locked, Green is where the physics scene is locked)
Kind Regards,
Wilco