At the moment, the only thing we know is that this appears to be some sort of bug with the new Season 1 update. There’s no ETA on a fix, but one is surely coming.
If you want a workaround, here’s how to invite friends on Modern Warfare 3 and Warzone 2 when it’s bugged:
Well, that’s all there is to it. Once you’ve sorted this out, why not check out the best Warzone 2 FOV option here or the best Warzone 2 guns here. You’re going to need to be well-equipped to deal with Al Mazrah. Trust us.