I don't know it's so hard to speculate ... but I know in the
pass past we
see saw somekind of a pattern where the hashrate are going on and off ... especially off in the first few days and the last days of a Diff.
Unless someone throw "new" hashrate it'll be at the end of the diff or at the start of it. (not always true ...)
It might be an old farm that buy a bunch of MW for a few day for cheap and it worth it to be turned on.
But it's probably someone testing hardware (Bitfury ?)
Speculating all the way here