Error on FBX import: Multiple Roots Found (but there aren't...)

Upon importing my FBX file, the engine kindly lets me know:
Error multiple roots are found in the bone Hierarchy. We only support single root bone.

(Yes, I left the spelling error in there for accuracy).

Here’s the catch: My character only has one root-bone.
Is Unreal finding bones that aren’t connected to other bones?

Attached a screenshot of my hierarchy: all bones and null objects are part of the root null-object. (I’ve also tried making that root null a joint. Same error).

Why is it complaining about multiple roots when there aren’t?

This model worked absolutely fine in Unity and I’m not really looking forward to having to re-rig and animate it.


{Bumpeedy bump?}

You probably already checked this, but I’ve got this message when I had two hats with the same name.