After nearly a month of playtime, there's a handful of "serious" problems that still have not been addressed. I would say that these are high priority fixes based on the overall quality-of-life problems they induce:
1) Vehicle "drop" locations for helicopters – this system needs a lot of work. Why can't the player just target where they want vehicles to drop within 50m? Even if there are collision problems, it can't be any worse than the nonsense/randomness that is there now.
2) Drone and binocular bug – this a highly game-breaking bug where the drone and binoculars can no longer be used and the only way to fix it is to quit to main menu and then return to the game. Seeing as many people play this like a stealth-action game on Extreme difficulty, it is absolutely inexcusable that this hasn't been fixed (it has been around since open beta).
3) Coop mission sync – the "Title Update 2" patch caused a lot of problems with missions in coop mode. Many missions just will not complete correctly and have to be reset and done multiple times hoping it works.
4) Weapon load-out and ammo – it seems like a big design oversight that weapons can be changed anywhere, anytime instead of just at ammo crates. Why even have ammo limits if you're going to allow this kind of system? Fast travel refills ammo too … this system needs a pass through the "stop being a fucking pussy" department.