Copying bone transforms in Metahuman Control Rig doesn't work in UE 5.6

In UE 5.6, it’s not possible to copy bone transforms (location, rotation) in the Metahuman Control Rig.
For example, when I try to copy the rotation of a bone using Shift + Right Mouse Button, and then try to paste it, I just get this: “()”, meaning it’s empty.
In UE 5.4 this worked fine.
Am I doing something wrong, or is there a new setting I need to enable for this to work?