From what i read on wowhead, it seems that if you have done the Cleansing Drak'Tharon chain in Grizzly Hills you get the Reunited quest instead of Dark Horizon.

Currently there is no such condition in the Questie database

8.0.0

@Yttrium-tYcLief corrected these two quests already and linked them:

Reunited requiring Suit Up!
and
Dark Horizon requiring Dressing Down.

I'm pretty sure I've already fixed this one... going to close as stale for now unless you can confirm it's still an issue, in which case I'll take a look