Yes, this has to be the problem. More evidence:
Zak M says: when we sweep a component in MoveComponent(), we only sweep the root component and then teleport attached children
That is really, really, really unfortunate. I need a workaround for this.
Can I somehow grab the collision shapes from the attached actors and move them up to the root actor?
Another idea would be to not attach the other actors and move them all individually (this sounds awful).
Is this something I could patch in the engine code? I’ve never modified the engine code, is it difficult?