For several matches in a row I haven't gained any exp and all players in-game are on level 1, at least on my screen. I tried to restart the game but it didn't help.
Exp and in-game level
You're not alone, several people are experiencing this. I'm not aware what is causing it or when it'll be resolved. Very sorry for the inconvenience!
I'm guessing credits for unlocking cosmetics are bugged too? It says I've got 400 in the customization menu, but when I click on "unlock" for a 300-credit item I get a message saying I don't have enough.
So partway through my night of playing I went from level 13 back to level 1, then started gaining XP again. Looks like my credits reset and unlocking is working as expected now.
Only odd thing at this point is my characters are all still wearing everything I'd unlocked in the first beta, but those items are locked for me now.