Could be a number of things, it’s probably rare that anybody got to such a high multiplier. The whole game is probably riddled with bugs like this, being a game jam result :) I might revisit this version one day, expand it and fix things.
Glad you enjoyed it though! Check out Schildmaid MX, which this game is kind of a demake of, that game has a lot more content and more fleshed out design.