Tried contacting Xbox support they told me to post on the support forums. I have beat the Seeker Championship 1st place in all races and all the points are unlocked and I have not received the achievement. People on TrueAchievements have also reported the achievement not working.
Have you beaten the Forza Drivers Cup?
Beating the Seeker championship doesn’t unlock the ELITE achievement only the normal one. You have to beat the Drivers Cup then complete the Seeker Elite cup to unlock the achievement…