The v5.3.1 Hotfix corrects an issue with a corrupt text file, which made it impossible to load a save in the 194 campaign if, in between the save and attempted load, you even started a 190 campaign. It could also have caused general stability issues in the 194 campaign. The Hotfix also includes some minor updates to Goguryeo in the 194 campaign that somehow missed inclusion in the v5.3 (Jian'an) Update, as well as fixing a few missing bodyguard models in the 190 campaign. This Hotfix is not necessarily required, however it is highly suggested to install.