Running a Nicehash AMD legacy miner on a rig with four RX 580s.

Every night between 2 and 4 AM something happens to the rig where it loses it's connection and stops mining. When this happens it can no longer be remotely accessed and requires a physical power cycle to get running again. Makes it a real bitch when you're 400 miles away from the machine.

Any idea what the problem may be? The log file says:

"No connection could be made because the target machine actively refused it 127.0.0.1:4000"

OK fine it can't connect whatever, but why would that knock the whole computer system offline requiring a restart?