Mastery Rank template showing on failed mission

[Fallowsthorn]

Failed the sortie, and instead of the usual failed mission info, I got this:

(It's hard to see but on the left and right it says "Text" and the white bar behind the whole thing says "MENU ITEM".)

I couldn't leave this screen (by pressing escape, by clicking, by trying to click where the "continue" button would normally be, by mashing random keys because why not), and eventually had to force-close the game.

I have no clue why this happened but it sure is weird.