Hey DavidLaid
Your REDSEC Ranked progression should be tied to the EA Account you're using, so if both your PlayStation and Xbox profiles are linked to the same EA Account, you shouldn't normally have Diamond I on one platform and Rookie/Beginner on the other.
The Elite Top 250 leaderboard is platform-specific, but your regular Ranked progression isn't expected to work as two completely separate ranks.
Since your cosmetics are already appearing correctly on both platforms, could you also check whether your Career Rank, weapon progression and stats are the same on PlayStation and Xbox?
Also, please check the Connections section of your EA Account and confirm that both console accounts are linked there. Don't unlink either account while checking.
When did you first notice that your Ranked progression was different between the two platforms?