Hello.
I would like to find an event (virtual method or callback) in which would have been aware of the disconnect from AttachParent and the same event for attach to AttachParent (drag/drop and change component’s parent at Details panel). Both events are interested for editor time and runtime too.
USceneComponent::OnAttachmentChanged and DetachFromComponent do not correspond to the expectations because it is impossible to correctly identify parent component (called many times with different parent).