Mixamo Thumb not Moving when mocap applied

Hi, I'm having an issue when trying to retarget mocap to a mixamo rig in c4d. No matter what mocap I try to retarget or what way I reposition the thumb in T-pose, the thumb never moves when the mocap is applied. Every other part of the skeleton moves perfectly so I'm not sure what I'm doing wrong. I assume there's a fairly obvious solution I'm overlooking but if anyone has any advice I'd really appreciate it.