So for some reason I found myself unable to start new games in vanilla CK2, v1.111 because they would crash on day 2 (Sept 16 1066). My checksum when this was happening was KUTD. I needed to do a clean install to correct the issue. I had tried to uninstall and reinstall previously, but had not realized that there were folders left in the Steam directory after uninstalling the game through Steam. Manually removing those folders as instructed by AndrewT in several other threads resulted in my next install having the correct checksum of MLYP. At this point, I was able to start new games again as normal.