Do you have a spare fan?
You could try changing the fan.
Trying a 4th fan now, what i have noticed is that the intakes are 2.7a and outakes 1.6a ?? No wattage on them but 32.4W on intake, 19.2W on outake...
I tried a 1.6a on the intake, i've had these spare fans for years from before you could just search Antminer fan on Ebay...They are server fans.
Fan is running MUCH faster visually now with a 2.7a on the intake, temps still hitting 101, 97, 97 though and thats at 550RPM fixed freq !! Boards/heatsinks are spotless ?
It is also now showing NOT showing a fan5 speed, as normal with only a fan 3 @ 3720 and fan 6 @ 3960.
Weird..
Ebay is a minefield with them, all differing amperage, differing CFM, differing speeds ??