Diff is supposed to go down to adjust to 10 min block time
I have no idea why hash rate would go down from 8400 to 7900. Bitmain testing batch 2?
I could make a guess that they put a lot of units online over the weekend for testing. There would be no other reason why the difficulty would keep climbing over late Saturday and all of Sunday. The last of the first batch shipments landed at peoples doors on Friday. Even if a handful were Saturday, no way that justified the levels of difficulty increase that we saw over the weekend. It was parabolic.
Well, Friday deliveries can be powered up on Sunday
Yes they could, but the Friday deliveries were the smallest of any of the shipping delivery days. Also, in this situation, do you really think many people got these things on Friday and didn't power them up until Sunday? I truly doubt it.