the stats command isn't working with teams
when you create a stat, like SuccessCount, and after this you join a Team, the stat will stop working, and will work again only if you set the stat again or leave the Team
reproducing the bug:
1-create a stat with
"/stats entity PLAYER set SuccessCount PLAYER scoreboard"

• the Player is your username and the scoreboard is any scoreboard created*

2- set the PLAYER scoreboard to 0

3- Join any team

the stat SuccessCount will not work, until you leave that team or set the stat again

I don't know the cause of the bug, maybe the team change the player name with colors and the stats don't update this.
this is a very bad bug and a lot of maps will not work with it