I've done a few, and no issues, however they were both hardwired.

I'l lean more towards the latency issues with zigbee and not the ip control.
I've had issues with zigbee, where volume on an amp will continue to ramp well after you release the button, i'm willing to bet it's repeating the signal.

Sorry, I have no solution. What does RTI say?

I can't wait till the new dual antenna remotes are released. Zigbee is super unreliable for us.