Whole rig moves down on transition between two animations.

Hi!

So, I am using a CAT rig with a Root controller imported in from 3Ds MAX, and after importing all my animations it all works well, expect that on the transition between my idle to walk animation the whole rig shifts downwards as seen in in attached image.

At first I assumed the root controller could me moving, but I watched the gizmo for the the root controlling in the work scene as the animation plays and it stays in place, I also checked in my max files if I have shifting, but in all the files neither the root or any other controller moves below zero.

I'm complacently stuck here and my final submissions in 3 days, any help would be appertained, thanks!