Yes, this can be caused by a bad CAN cable, electronics etc.
What color is the indicator light on the missing module and is it blinking? If it is blinking - power cycle, do a forced cold start or possibly load firmware.
Check the CAN cables.
Does Lab advisor see all the modules?
If that doesn't work you will need to call your local service group.
In one case the module indicator light was blinking. When we power cycle the unit the communication was re-established. In other cases the light was yellow as "not ready". We check CAN Cables and are ok.
We are controlling the units by Empower 3. It is was suggested that can be a problem with LAN/CAN Repeater that was locked up buy, How I can check that?
My Firmware is A.06.50 and in some pump A.06.54. Since this situation happened without an apparent cause I was thinking if that can be a "bug", something random.
We once had an issue between autoSampler and vial chiller on our 1200.
The motherboard of the vial chiller had been replaced and there was random communication errors which made the autosampler disconnect all the time. A computer reboot was needed.
The only way I could fix this issue was to install the vial chiller on our other 1260 HPLC. Don't know why, but on the 1260 I never got a miscommunication error again.
It's not really a true answer to your problem, but if you had an electronic part replaced lately, it could be the same issue...