Sounds like a clone file was used on all 5. I would highly suggest having a tech do an:
"Altboot, no data backup, no clone to .05000 firmware" Then setup 1 printer manually and verify the issue is resolved.
After a few days assuming no issues, have the tech come back on site and do the same to the other 4, but in that 2nd case, he could then apply the Clone of the known good configuration to the other 4.
The issue described has been seen on the Connectkey family quite often in the General Release firmware, but they have all been thus far resolved via the listed method of updating. The manually setup is a pain, but it is the only way to be sure, there is a real issue where you have 100% of machines running into the same issue on 3 different levels of firmware so there has to be something different in the way they were setup.
This is the .05000 release for the 7970 if you need it again