I think, we have exhausted all related settings. However, I suggest that you open a support ticket and attach a complete backup, so that we can check all settings.
Have you, by any chance loaded a loop (mono or stereo) into a slot by mistake? If nothing is plugged in to the send/return(s) then there will be silence. I have my loop locked as I generally use other gear as well as the kpa. When I use the kpa alone I still have that heart stopping moment of no sound. Just a thought.
