Chests Available Bug

Don't get my rewards when I get an S+ , S or S- Yesterday I got S- with Blitz and didn't received any reward, and a friend did at the same game.

Today, I got another S- with Blitz and I didnt got the reward again, I think it is a bug? Or do we have a certain chance to win it when getting the S?

Please help me, I really want those chests :/