Having problems with models sinking in on themselves

75921-idleposebroken.png

Our model seems to sink into itself when imported into unity, but only on a couple of animations. For reference here is the model in the inspector. It only appears to break once we put it into the engine.

Is there a scale value of any bone during those animations?

OR - how is the rig setup? Like normal - the spine is a child of the hip/root.

Or - are those animations optimized upon import?