As always, one of my rigs started to act up whilst I was on holiday. One GPU would start showing 511C errors, crash the miner and the rig within a few sec. Seeing that this couldn't be fixed remotely I cut the power to that rig completely using the tp-link smart plug app and decided to address it when I got back.
It was quite an easy diagnostic:
https://flic.kr/p/ETFBZzFlimsy Chinese risers. Always make sure you got a few spares, and don't insist on powering up a failing rig remotely if you suspect there's a hardware/power error.