Same thing happened to me.
I was in a full league since friday, looking good to stay in diamond in the run up to the Sunday promotion, then after the end of the league this:
No rewards, and only one guy from the league showing up on the board. I can't be certain, but I'm reasonably sure that guy *was* already in the league before the bug hit. It looks like the league is being cleared for next week before the reward system runs, and this guy was lucky enough to finish a small run in the time between it resetting and the actual reward handout. That said, that's nothing but guesswork.
I'd really like to get all my ammo colours finished so I can stop tryharding, a fix would be great.