What is causing my bones to display irregularly?

'm working on a character animation, and on a test render I noticed a part of the model was being displayed incorrectly. I opened a previous version of the file, which contains the same animation, and the same part of the model, with the same exact rotations and coordinates, but this one is being displayed correctly.

In the newer file, I didn’t change anything about that animation recently (was working on the environmental aspects before I noticed the bad thumb) so I’m at a loss what could be causing this. I also tried to manually place the bones where they belong, updating the pose library, applying the pose back into the scene and getting the same result–it just pops back to this weird position.