Attached Link: BVH mixer

Assuming you're using the Carnegie Mellon set, I downloaded one of the ZIPs (set 13) and took a quick look at some of the BVH files.  The problem is immediately obvious, in this set anyway.  The initial value of Hip Ytran is 18!

 

Try locking the Hip.  Or try my old BVH Mixer python, which lets you deselect and/or scale the action for each body part as it reads the BVH.

 

Later thought: in the animation keygraph you can set individual parameters to Static.  If you set only the hip Ytran (not the entire Hip) to Static before loading, the problem may disappear.

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