Posted this in another topic similar to this issue and will do so on this thread, in hopes of EA/DICE coming up with a solution to this:
They need to fix this issue. I just got the 100% completion on Xbox Series X/S version of BF 2042 without issue, and when I loaded up BF 2042 (XBOX ONE) version of the game to get another 100% completion on my account, the "Wheeled Warrior" achievement remained bugged. I even went the extra mile and got another vehicle to T1 Mastery from scratch, and the achievement refused to pop. I'd rather not have to unlink my account and risk losing all progress on the battle pass for the Battlefield 6 release. I've supported EA across multiple accounts, along with my family doing the same and wish small issues like this would get fixed. Otherwise, what's to stop this from happening on future titles.
P.S. For those that did the link/unlink method that Carnifex91 posted, when you got your old account back, did you have all progress on weapons/stats/battle pass unlocks etc available? I ask since I'm a few tiers away from completion on the new Road to Battlefield 6 Free Pass and do NOT want to have to work on everything from scratch, especially not that the game is close to 2 weeks away from release.