Does it happen to 1 of the 4 1080ti rigs or all of them? Enough power for those rigs? Unexpected reboots can be due power supply not being able to handle the load. I have mixed rig with 1060, 1070, 1080 and 1080ti and it works without restarting, sometimes there is a problem with the miner but watchdog can handle that. To me looks like that you have some hardware problem. Does it work stable with other algos?