Hi there, @nightfire525! Welcome to Discussions!
Congrats on completing every mastery challenge on Gold! That's quite a feat. I'm sorry to hear that your achievement didn't unlock though. Can you please try going through these troubleshooting steps here first? If the achievement still doesn't unlock, then the next step would be to try these connectivity steps, just to make sure there isn't anything preventing the game from updating achievements properly.
If the issue persists after going through the troubleshooting, it would be helpful if you could please provide a video/screenshot showing that you earned enough medals to get the achievement. Please upload the video to a website like YouTube (as unlisted or public) and share the link with us here. Thank you!