PHAT Does Not Generate Constraints

I have a simple model with three bones, each with a vertexgroup weighted to it. I made this in blender. I import it into UE4 as a .fbx. I open PHAT to edit the Physics Asset. I add three capsules for collision, one on each bone, as shown in this tutorial:

However, unlike in the video - no constraints are generated when I add the new bodies. You can see in the top-left of the video that when the thigh capsule is added, the count of constraints increases to 1 - when I add bodies, that counter stays at 0.

I have “add joints” checked true, though I don’t know if that’s related.

What do I need to do to keep my skeleton constrained?