Rune Page is an Empty Window

When opening up the rune page to customize my runes, the only thing I can see is an empty frame. I can still see the champion pool (this is in a game lobby), but can't click on them because, ostensibly, there's an invisible window in the way.

The only part that is visible is the very top border of the window and the X to close it. I wasn't able to change my rune page for the match and had to settle for one of the premade pages, though it was definitely suboptimal.