Thanks for the help guys. I'm still testing, but here's an update from your suggestions:
I experienced the freeze up even after deleting every control surface from my list. This last one happened when I assigned one of the XY sticks to the Cutoff and Resonance parameters on the RetroSynth instrument plug-in and started moving the stick around. It was controlling the parameters fine for a few seconds, then the keyboard froze and stopped functioning.
MIDI Monitor readout looks normal from that moment. It was sending CC 71 and CC 74 controller messages, which that XY stick is set to control. (MIDI Monitor lists those CC's as "Brightness" and "Timbre/Harmonic Intensity")
I power toggled the keyboard, performed the same steps, and I'm not able to reproduce the freeze-up, it just works now.
I also just realized you mentioned to toggle the "Bypass all Control Surfaces" setting. Just turned it on, so we'll see how that fares. However, it looks like this means I won't be able to map a knob (or an X/Y stick) to any controls, huh?