Recently had the same issue with 2 different customers who have been running the same system for 5+ years.
The systems have an MD4 and 3 MC3s.
After a partial touchscreen failure the customer replaced the original MD4 (running a program written in IQAN design 3) with a new MD4 and flashed the whole system with an updated program written in Design 5.07.
After flashing, everything worked for a few days and then one of the MC3s had a No Contact error. I had them swap two MC3 modules around and reflash and the MC3s received the program with no issues over the CAN network but the No Contact message remained. I had the customer check the indicator flash codes on the modules and the 2 units that could still talk with the MD4 were flashing 3 reds and an amber (no contact), but the MC3 that couldn't be communicated with was flashing steady amber (status ok).
I then had them unplug the C2, C3, and C4 connectors to the MC3 causing the issue and the No Contact went away. I had them plug in the C2 and C3 connectors and everything was still working fine (besides open load errors from the outputs on C4 connector). When the C4 was plugged in the No Contact returned.
The system uses Digital Out/Returns on C4 pins 13/14, 15/16, & 17/18 to control relays. Once they unplugged the wiring from those 6 pins the problem was resolved. The functions run by those relays are not critical to the operation of the system so customer is leaving unplugged.
As I said, this is the 2nd time this has happened recently. The first time I chocked it up to a wiring fluke but now that it's happened twice and both soon after a screen replacement/firmware update I'm starting to connect the dots and thinking there may be a bug in IQAN design 5 which is causing this issue.
Customer support service by UserEcho