after a game the earned XP is added and i level up from 19 to 20. then while waiting to join game i am awarded XP for an achievement which causes me to level up from 19 to 20 again. and therefore losing XP from what i can tell. P.S. the levels used are just examples, this has happened multiple times.
This is just a weird bug between leveling up and earning achievements. There shouldn't be anything wrong with your level or xp.
