What is the model of the S9?
If it is an earlier model or a model without the auto tune firmware, you may want to try to flash it with the newest firmware. Or even try to re-flash it with same if it already contains the latest FW. When it comes back up for the first time, it will let you set the frequency that one time. Set it to the frequency it is supposed to run at.
I'm not one to randomly suggest flashing miner firmware. My thoughts are if it ain't broke, don't mess with it. But in your case, it is broke. So what do you have to loose?
I flashed a flakey older S9 that was showing random X's on all boards no mater what frequency it was set to. Amazingly, the newest S9 firmware took care of that problem and the S9 is still hashing away at its stated frequency after over 3 weeks with no X's.
The new firmware will raise your PCB and chip temps by about 10c. But I have had no issues with mine since flashing.
If you try that, let us know what happens.
Good luck!!
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EDIT: A note of warning!!! After flashing, it MAY take as long as 30 minutes to come back up. BE PATIENT and wait. The new firmware takes a long time to start up each time it is powered on. Again, BE PATIENT and don't try powering it off.