Bug or what?

So i pushed that new Sirius challenge (where you win 1 battle per brawler) up to 35 or so. I collect the 2 rewards, take a 20 minute break from the game. And when I came back, the bar went down to 28, and it didn't take the trophies away, it didn't even take the reward back, but of course it won't let me collect this 33lv reward again.

Is this happening to anyone else? Should i keep on pushing or will I just get sent back a few wins every time?