So i'm having the same exact problems.  I've opened a ticket and still waiting, as they only reply once a day, it's like watching snails crawl.

have either of you heard back from bitmain on what's happening here?

I'm getting a reading of 0, and now it has resulted in one board beeping and stoped hashing altogether, it only resumes once i disconnect that board.  But i'm afraid others will follow.

I've updated the firmware, and tried any sort of reboot i can think of.

i have also increased the fan speed to 100%  and nothing works