Well, we can probably rule out Abyssea at this point. People have been infesting it since yesterday and no reports of Plates dropping. Most likely candidates are Voidwatch or WoE.
They could be timed pops in Abyssea, or even from some new quest or other. Can't rule it out for a few days until people actually find out where they come from. Been noticing JP players mass killing a lot of usually left alone mobs too (and swapping regularly between mobs etc) so either they know something we don't or they are just all mass testing.