As I read your temp value, there are 3 values in a row: 43 47 50
As I understand it, the 1st of those three values is the temperature of the Controller (not the Pi) within the A6. When that exceeds 40C things get squirlly and it's usually on it's way to shutting down. That seem consistent with your observed behavior. You need to make sure the controller stays cool. Possible options:
1) Supply cooler air to the A6 intake (end with the PCIe power cables).
2) Some folks have considered laying the A6 on one side, possibly upside down.The controller is at the top.
3) Any obvious obstructions at either end for the fan?
4) Are you running either the Delta or Sanyo Ace fan?
5) Are you pushing the input 12V to get a better hash rate?
The short summary is that the controller is TOO HOT (I think).
1) Can't, running A/C is not doable so i use outdoor air
2) Thats worth a try but it work just fine if i set the fan speed so that temp never reach 76C in the first place, so the controller protection preventing fan speed to raise seem kind of a bug, if thats it.
3) No they are being cooled fine and work fine (if the fan are set manually), its the automatic fan speed that is going haywire.
4) Stock, i think its Deltas
5) No its ATX PSU and they are underclocked to keep RPM at 3k (noise), if i set minimum fan speed over 3k they hash fine without the issue, but if its for example 2.8K when they reach 76C after a while, they shut down and go 100% fan speed, instead of raising the fan speed.
My ambient temps is always between 28-33 and I never had one issue with my AV6 BUT my first temperature never go over 41, currently at 39.
I dont know why the controller isint getting air or why it would prevent fans from spinning up, though.