I've had a few miners and I've personally never seen the hashrate/difficulty double in the space of a couple of hours upon a new miner release or manufacturer testing. The fact that vertpig has gone offline due attacks makes me think it's an attack but I can't find anything official from mona or vert.
This same thought crossed my mind. Literally every Lyra2rev2 coin hash rate doubled or tripled in a very short time (from like midnight to 3am). That is insanity and makes me think something else is going on. Maybe it is bitmain or some other manufacturer testing out a bunch of miners, or something similar, but it seems like a good way to wreck future earnings since coins will be much more likely to fork if they see this behavior...
So I am thinking it is some sort of bad actor trying to attack the coins.