Not getting loot from legendary mobs
Sometimes, it seems like if the champ or legendary is associated with an event completion, its dropped loot is buggy. The chests are fine.
There are several examples of this out in the PvE world. The specific one that comes to mind is the champ golem in one of the Asura labs in Brisban Wildlands. I’ve never gotten a single drop off of him, even when solo’ing the entire event.
With the Viscount and Lich, I have occasionally received loot from them, but it’s inconsistent.