Losing Hextech chests?

I don't know if this is a visual bug or something, but I happened to notice that last night, I had 8 chests in my inventory, and 2 "available". This morning, I got enough shards for a key, so I unlocked a chest, bringing it down to 7 chests. In between last night and today, I have played several games, at least two of which I got an S on. I happened to check my profile and I have no more available chests, but my inventory still has 7 chests.

Note: the champion(s) I got an S on were already locked for this season, so I'm not saying I should have gotten a chest, just that I seem to have "lost" two potential chests.