We're aware that players who have played on multiple platforms can show on leaderboards numerous times.
At this stage, Respawn's API system (The system from which we pull stats) doesn't inform us which platform the user played the most recent matches on, so we cannot simply 'set a main platform' for the user accurately.
Sadly this means we will likely see duplicate entries on all leaderboards that are not 'Platform Specific' such as Ranked Score.
Apologies