LDoN Assassination Missing Boss

L65 Hard Guk Assassination (Drowned Crypt) doesn't spawn a Boss. No emotes, cleared zone, nothing spawned. After clearing I zoned in ranger and spent 20 minutes running around visiting every room multiple times, ended up with nothing on track and nothing to do.

FWIW the assassination text on expedition is as follows: "There is one creature called a Witness of Hate lookout that must be killed so we can slow the proliferation of the curse." It's weird to begin with; that it's not a named mob like other 'Single Mob' adventures, probably should have clued me in to decline it /sigh.