I have the same issue. I believe that chip is not correctly reporting the temp and it's not the actual temp. I've also seen it go to 20 before just by changing the ASIC voltage. (And not necessarily on that chip, they all kind of affect each other). So if this chain or any of the others don't have HW errors then bump down their volts a level (just 1 chain) and see if that fixes the temp. or if a chain is getting more than 1 or 2 HW errs a min, bump it's level up.
Hope that helps.