I bought 25..and Love these!

I have 24 humming at 4-5 mh/s and have been hashing at 105 Mh/s...I love these beauties.
But almost since I've gotten the latest 12..I have one that won't hash at all and one that consistently runs at 17% hardware errors.
I haven't tried to dial up the voltage on the one with the high errors...but any thoughts on the one that won't hash at all??  I've tried switching hubs and changing the Hz...but to no avail.
I'm running the whole pool at 796hz out of the box..no adjustments.

Thank you in advance!