I tried this with multiple models and very simple ones as well.
Steps to Reproduce:
Initialize Character
Join Animations and select a batch of animations. These will import correctly.
Join Animations a second time and select a new batch of animations. Any existing animations will now be bugged and it will appear as though the hips are locked on the Y axis. This is most noticeable with animations like a "fall" or "jump".
Temporary Solution:
Import ALL animations at once. (This is fine for now, but it would be nice to be able to import in batches for performance and testing.)
I tried this with multiple models and very simple ones as well.
Steps to Reproduce:
Temporary Solution: