I’ve just started separating my current level into multiple sublevels and have hit this problem when I try to move an actor to another level when it has references; it’s impossible to tell what’s referencing it.
To make it worse, if you click ‘no’ to the question about deleting it, the object just gets silently duplicated which can be almost impossible to spot in a large level. There needs to at least be a ‘cancel’ button that just does nothing - don’t move the actor to the other level at all, don’t delete it, and definitely don’t duplicate it. That’s the behaviour I expected the ‘no’ button to have.