Unscheduled Server Maintenance

I wouldn't abuse it if I were you0.o Could lead to a possible ban.

I don't think it's a glitch.
Cassandra says "keep bringing me flowers" or something like that, not "bring me more tomorrow" or "in an hour" or anything else that would imply they intended to put a restriction on repeatability.
I do agree unannounced continuous 2x drop is rather odd, but maybe they are hoping that people buy lots and lots of 2x drop cards to make the best use of this unexpected bounty.

But it's free 2x drop. We know we've been dying for that ridiculous soul driver.

Mmmhm. Just a heads-up, if you're still in the Lunar Dews stage: Ariant mobs do not drop the event items Cassandra wants, but Magatia mobs do.