I don’t know much about the topic, but from what I’ve been researching, some animations can present jitter due to the plugin, so it’s possible that’s the issue.
If you have Blender, I’d recommend trying to export the animation as I mentioned before to rule out that possibility. On the other hand, in that post several possible solutions are mentioned that you could try; maybe one of them helps you resolve the jitter.
In my opinion, it could be a problem related to the bones and/or the root but I can’t think of any other solution.