Game appears twice under achievments

Not possible at all. The only way to remove it from the list is if it only had 0 gamerscore earned.

Did you happen to play 2 different region versions of that game?

That 50G, did you unlock those same acheivements for the 1420G or are they different acheivements?

Sorry about that, Ben. If the achievement appears under “Locked Achievements,” either the achievement was not successfully unlocked, or the console hasn’t synchronized with the Xbox network. If it hasn't appeared after 72 hours, try unlocking the achievement again or contact the game support for further troubleshooting.

Solution 2: Check your achievement progress online

You can check the progress of your achievement online to verify that your console has synchronised with Xbox Live.

To view your achievements online:

1.Sign in at xbox.com and select Achievements.

2.Select the title of the achievement you're trying to unlock.

3.If the achievement appears under “Achievements,” it's already unlocked.

If the achievement appears under “Locked Achievements,” either the console isn't yet synchronised with Xbox Live or the achievement was not successfully unlocked.

Thank you for the information.

Kindly try to check the progress of your achievement online to verify that your console has synchronized with the network.

To view your achievements online:

Sign in at Xbox.com.

Select your profile icon in the upper-right corner, and then select Xbox profile > Achievements.

Select the title of the achievement that you're trying to unlock.

If the achievement appears under Achievements, it's already unlocked.

If the achievement appears under “Locked Achievements,” either the achievement was not successfully unlocked, or the console hasn’t synchronized with the Xbox network. Allow up to 72 hours for this synchronization to take place. If it hasn't appeared after 72 hours, try unlocking the achievement again.

For the reference link: https://support.xbox.com/en-US/help/games-apps/...