4th 1080ti has low hashrate. how's that???

[Ruso21]

I think I read somebody's post  with the same problem but I can't find it...

I have 4 Strix 1080ti using GPU Tweak II (no afterburner because had problem with the fan speed)
GPU Clock +80
Memory Clock +440
Temperature 71 / 69 / 64 / 45

as you can see... the last one has low temperature and low hashrate running at 270 sol/s while the others has 720~745 sol/s
I'm using mining pool hub with awesome miner.
and yes, I have enough power. Using a 1350w Platimax connecting 1 GPU per slot.