According to Velkort, someone (again) transformed the Magical Alter in Serbule Keep into a Necromantic portal to another realm. A variety of Undead creatures poured forth from the Alter anytime it came in contact with a source of Necromantic Power.
A series of magical locked chests spawned around Serbule Keep. Skeletons and ghouls drop keys to open these chests. After a time, the Magical Alter returned to normal, but keys continued to be dropped by various species of the Undead.
October 29, 2016 - November 5, 2016 (Alter returns to normal) - December 5, 2016 (Chest keys stopped dropping).