I have noticed that in my time playing the game, I have jumped ahead levels a few times. Once I jumped to level 3, and I didn't think too much of it because I figured I might have just leveled up another level. It was after my first match after all, so I could have earned enough experience to level up twice I thought. Quickly though, I noticed that I didn't get anything for leveling up to level 3. I shrugged it off as a game bug.
More recently, I leveled up from 5, to 6. With just barely enough XP to make it to level 6. However, once I reached level 6 and it displayed my rewards, it jumped up to level 7. It then displayed the exact same rewards I got for level 6, but when I checked, I didn't get an extra 100 credits.
So I've found that now and then, the game will boost you up an extra level, and that extra level it boosts you doesn't even give you a reward.