Just to be sure, back up comms are working, but once the CNI is set to UFC you lose UHF?
Just trying to make sure I understand what you are saying.
If it does not work in either, I would say check the Comms 1 volume knob to make sure it is turned up.
Note: If COMM 1 knob is all the way left, UHF info will be absent in DED with CNI set to UFC.
HTH