Yup to the above posts.
The thing is rated for 7a/pin, but there are a number of things that can reduce that number and cause heat buildup.
Heat buildup in turn makes the issues worse, which leads to heat buildup, etc.
Given the age of the board involved in that picture (a Rampage II Extreme, I believe) and the wattage of the CPUs involved (which go >200w easily, but >300 is a stretch) I bet there were connection issues.
When you're subzero the connector is being actively cooled by the PCB under the CPU being far below zero. That spreads via the big fat VCORE/GND/V12V copper planes and cools everything in the general area. That's the #1 issue when it comes to long term (>5 minutes) extreme cooling really, the cold spreading.
(Yes, I'm aware cold doesn't exist and it's heat transfer, but that's a clunky way to talk about it)
They do burn up from time to time anyway, but not on modern stuff for the most part. There aren't any modern chips that can match a Nehelem or Gulftown for raw power consumption these days.