The most I can get out of my two Batch 2 machines is 687 (although 681 produces a higher hashrate) and 625. Anything over that and the third hashboard on both machines goes to 0 hashrate.
i just recived my 2nd batch. mine too. 3rd chain die at 681 or up.
What hash rate are you getting at 681 or close. Do you get hw errors on any chains or does it just hash at 0 when you go at or over 681