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1. Whoever is hosting the xp lobbies the xp will not stick at all. When you exit the game you may think its stuck but it hasnt. Once you go back to main menu its gone.
2. As for the host. If you want your main account to get stuck get a friend with good connection on that account. Then you can host on a dummy account and then let your friend get 1 kill. You will then leave the game and it will migrate. If it migrates to your friend its stuck. All he has to do is leave.
3. Once it sticks for your friend tell him to go to main menu. This is because if you dont go to main menu after every modded game you will find yourself back to say 3rd prestige once you've just done about 1 hours worth to get to 15th. You will be pissed off. Once you come back from main menu just prestige and do the steps again.