First: if an S9 doesn't sense both fans during startup, it will shutdown or just go into an endless test loop.
Obviously not all fans are created equal. If its not sensing the speed there is likely an incompatibility. The S&H is high, but Bitmain sells replacement fans for a reasonable price.
thx for the reply....
i gotta few different makes as well as ones the same but having issues with them all

i think i might have some errors due to faulty chips tho, with two remaining working boards i both get Asic[29] & [57] with rather high values, odd that its same chips?
also 63 chips per board but seems like on 62 are being recognised on both, im out of warranty too now, seemed to happen just less than 1 month after it expired too

for anyone who is reading, dont update with bitmain firmware!