Same issue here. I signed a treaty with a Vlandian lord (not the king, just a random lord, but he was a commander of an army) as a leader of the new Calradian Empire. I payed a good amount of gold to them. After the dialogue screen, I was returned back to the world map, and then the game crashed. The crash report was as the following (I was able to obtain this via Bannerlord Tweaks mod, which provides a crash report):