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.
That is really interesting, I wonder what is the difference? Mine has been ripping along at 750 for over a month without any problems. It has been an impressive little machine.
And you are not the only one who seems to be having issues with batch 2. And probably can't open a support ticket since you technically voided the warranty by OC it.