Weapon Challenge not Unlocking PSR

I'm experiencing the same issue as many others where a challenge shows completed but the reward is still locked. For me, it's the 'Deadeye' challenge that shows complete on the challenges menu, but the rifle is not unlocked in my inventory. The other reward for the challenge, the 'Crackshot' title, is not unlocked for my profile. I sent a request for help from EA Help, but received only a very unhelpful reply that I don't really understand. This is a quote from the email: "Load up the dedicated feature mode associated with your challenge."  Like, what does that even mean?