Hi Ben! I had the exact same issue, had a character cheering and fist pumping into the air, and the fingers would explode every time. Try increasing the Substeps. I had to raise mine up to 12.
Here’s a post explaining what Substeps and Iterations do:
https://forums2.ragdolldynamics.com/t/substeps-iterations-retargeting/271/2?u=isai