Firstly, thanks to the wiki contributors, else I would still be stuck on this!
So, not sure if a bug, but my suggestion is for some meaningful dialogue and quest log please.
After talking to Mayor Vandus, the quest log simply ticks off "Locate signs of the Traitor Gregory's flight". There's nothing after that, no clues, nothing. As you head south, you can talk to NPC's along the way and they will have dialogue about him, but no quest advancements. The quest advances when you talk to Sergeant Borash in the deep South (21676/19872ish), but there's absolutely nothing to tell you that he is the NPC you must talk to in order to advance the quest. Could you pretty please make the step "Listen to Sergenat Borash" visible before having actually talked to him?