So I've taken a look at a couple games now and it seems like other people are having this error. I think perhaps it is happening to WebGL builds from newer versions of Unity (personally I am using 2020.1.6f1). When you build and run the game it works perfectly fine. However, when you upload the game to Itch.io it will never finish loading. I was able to fix this error by going to Project Settings -> Player -> Publishing Settings and setting 'compression format' to 'Disabled'. I hope this helps someone upload their game to Itch (although sadly it won't be fixed in time for judging).