You are going to need a tech, according to this thread and the other one:
Firmware was updated, Fiery was updated (and this certainly isn't a known issue to the device)
So it isn't software/firmware
It isn't settings, you confirmed every single setting that matters for this issue are not/were not incorrect/changed.
So it isn't settings/firmware or software
Which leaves an actual (really odd) hardware failure. Hopefully simply the crossover cable connecting the 2, but that isn't likely.
The only other option is a complete reload of the Fiery and an NVM wipe of the copier if that isn't enough. But realistically, we've covered all the settings that may have been changed