Hextech Chests no longer dropping?

Is it once, ever, on certain champs? Because I haven't rotated champs much in a long time but ALL my chests are available.

Otherwise, I haven't gotten any chests and all 4 of my chests are available and S has been had several times since the first "chest available!" was up and I was on, what I THOUGHT, was a different champ than the other 3 recent times.

Now I've got all 4 chests up and no chests have been dropping despite S ranks occurring.

What the hell is going on? :<