Critical Error Has Occurred?

So occasionally when I play ranked, I get this error that will freeze my game and force me to close it. It has caused me to lose 2 games already, and I'm getting sick of it. I think this has only happened since I updated to 8.21, but I've had problems of League suddenly tabbing out regardless. It seems to pop up once every 4ish games, as I've only gotten it twice, I can't for sure say. Also I took this picture from another board, but I can't say yes, due to it popping up in the middle of a ranked game.