Submitted a bug report on this (#260721-002419 and got the usual "Go away, kid. You bother me" (sorry, "Thank you for your feedback") and a closed ticket, but I'll reference that here and add a bit more information to the issue. The ticket was specifically for Urcelmo's mission, but after having completed all three of the #5 quests, it applies to all of them. The quest targets (Jurak-dar in Reaper's March, Short-Tail in Rivenspire, and Mizrali in The Rift) pick up a second quest marker once you get within ~40m-100m of them. The distance varies depending on the target. Jurak-dar's white marker got lost at almost exactly 100m away, but Short-Tail's got lost at about 40m and Mizrali is inside a building with a transition, so no guesses. The normal white active quest marker shows from a distance, but once you get close enough they also pick up a black inactive quest marker, which unfortunately sits in front of the active marker on the compass. So when the player gets close enough, they lose the white marker. I have not noticed this with any of the earlier missions and haven't done the later ones, so I'm only sure about #5.
I can maybe point to one potential cause, however. Jurak-dar has a side-quest in Malabal Tor, so my initial thought was that he was bringing that quest-marker with him and I don't believe that the character who did the Freerunner mission had done it yet; they kind of just bee-lined through the Dominion for Cadwell's Gold and skipped most side-quests. Mizrali only has one quest, Holgunn's mission is to do that quest, and I know that the character who did the board mission today had not completed it. The fly in the ointment is Short-Tail. She only has the Freerunner mission for Arabelle and I don't think she's even in Northpoint unless this board mission is active. It's not a game-breaker by any stretch of the imagination, but it will undoubtedly cause a few "WTF?" moments for others.
And having done my bit for making Tamriel a nicer place for other players, the kid will go away and stop bothering you (for now).
I'm fresh out of outrage, but I could muster up some amused annoyance if required.