Why would an S9 auto-tune to a lower frequency?

[fyoung55]

Any ideas?  It's a December 2017 batch. The S9 used to auto-tune right in at 13.5 TH/s (Freq at 638, 631, 612) now it auto tunes to 13.1 TH/s (Freq 627, 606, 589)  Temps are the same, but the fans are running a bit faster.

[Raymond_B]

Any ideas?  It's a December 2017 batch. The S9 used to auto-tune right in at 13.5 TH/s (Freq at 638, 631, 612) now it auto tunes to 13.1 TH/s (Freq 627, 606, 589)  Temps are the same, but the fans are running a bit faster.

What are you using to power it and what are the temps?

[fanatic26]

If you have the November 17th firmware I would recommend you roll it back. I roll back the firmware to the 4/29 release and it solves all the strange issues I have with the last 3-4 batches of s9s.