Besides the Obvious, Make sure the latest firmware. Any cabling termination rj45 be checked for defects. 1 node or device can create a broadcast they may be knocking out the others. Is all the devices on the same network that are affected. The ones not affected on a different network or the same. Are these on a switch or daisy chain from the controller. If on a daisy chain from controller I suspect the first inline that the trouble starts to be a suspect.If that one loses power or hickup it will affect the other downstream. Are you using the PINO_DEV_COM instruction and you may be able to see any faults accruing in the fault table may tell you also.