Wow that triggered something in my old brain, though I can't remember exactly what it is called I know there was a proprietary functionality on some Yamaha keyboards that had caused issues in some virtual instruments/plugins. I wonder if the CMI built-in proprietary tech (I think it is called U-CONTROL or something similar - ah, looked it up it is U-CTRL) is confusing SampleTank 4 in some way? If this may be the case and if there is a way to temporarily disable that, I'd recommend trying that. Not the optimal solution if you use this U-CTRL functionality but for troubleshooting purposes it is worth a shot.
Edit - looks like a nice controller, by the way.