Thumbs are importing incorrectly. This problem "may be coming" from an extra bone that Reallusion doesn't process well. I didn't have this problem until recently when I upgraded my mocap system. At that point, the "Claw hand" appeared. I've tried several solutions, but as I studied I noticed an extra "Bone" in the Thumb. I'm not sure why it's there. According to our anatomy we only have 3 bones in the thumb, not 4. So if we consider the base bone, we will always have 1 bone less in the Thumb than our other fingers.

This could be an issue outside of Reallusion since technically mocap data is not completed by Reallusion. However, iClone is advertised with an easy to use workflow and this problem persists throughout many user workflows. I'll be reaching out to my mocap solution as well. Hopefully the notes below can help Reallusion solve this issue. It seems like it could se solved easily.

This issue has been on the forums for quite sometime. You can reference a few notes on the issue in the below links:

https://www.reallusion.com/FeedBackTracker/Issue/Thumb-issue-persists
https://forum.reallusion.com/283800/Thumb
https://forum.reallusion.com/514433/Mocap-Fix-for-this-issue-since-iC7

(I tried to add my notes to an already posted issue, but the system wouldn't allow me. - sorry for a second post.)