I did some reading, since I don't yet own any Unicomps. This might be helpful:
Model M Troubleshooting FAQI have heard of Unicomp controller problems. Maybe your usb controller isn't suppling enough amperage to the tempermental keyboard controller? Maybe you could try a powered USB hub, other ports/controllers/computers, etc?
I know
jacethesaltsculptor would know more. He uses Unicomps a lot, and I could have sworn he had some controller problems himself.
Maybe you should reach out to Unicomp as well. I have heard that their customer service is fantastic. Based on my only exchange with them, I am inclined to agree with the sentiment. They forgot one of the keycaps I ordered for my F77. I sent them a picture of the unopened bag and they quickly sent me tracking information for the missing key, no questions asked.