I would like to suggest one other possibility if you have a very manual procedure, use MSI AB and you are a tired solo operator.
It's possible on a fresh system reboot, if you use MSI AB to set the TDP and accidentally omit running MSI AB, when you run whatever mining software you are using, you are running your GPU's flat out.
Thank you for your comment.
I've had this in the past: forgot to lower tdp with ab. Luckily my PSUs detect overloading, and it shut off power.
In this case however, the system was shut down or in the process of shutting down, putting an enormous load on that one power cable to the mobo.