Hi Chris-
I've also read the replies you got over at Controlbooth.com and I think the audio cut-out is at the head end. That you could see/hear it at the mixer means you can eliminate all *hardware* that comes after the mixer as part of that problem.
Your video problems are likely related to the use of UTP for the HDMI converters (I've only used them on the output - display and projector side - and wasn't aware they would work for cameras, we usually convert to SDI for that).
That you could not replicate *any* of these problems back at the shop is frustrating.