If you change your Minecraft username, you should fully log out of the game and then back in before playing again.
64
142
1
279
@MojangSupport @Dinnerbone I lost some of my ranks on servers
1
Replying to @GappleSmacked
@GappleSmacked You will need to contact the server owner for help with this. ^HN

Feb 5, 2015 · 9:59 AM UTC

1
Replying to @MojangSupport
@MojangSupport Ok, I did and I will get my rank back shortly :)