Yeah, it’s not the bone groups. I would check that plane. I’ll try to reproduce that and get back. If the plane is the direction/root motion control, unparent it from the model and parent it to the skeleton. if not, what is it and what for?
Actually, scratch that, I see why. You did a retopo of the model using a plane, and there are vertex animations. If you parented and unparent the skeleton to the model, it makes new vert groups. Every time you unparent a skeleton to a model, you have to go into the vert groups and delete the prior groups made by the skeleton. Do not delete any vert groups you made on your own, just the ones made by skinning the skeleton to the model.