Summary: Crash when destroyed kingdom tries to offer vassalage, this time with a fresh save with no mods installed, the game will still crash, so no, it wasn't related to mods being installed the first time.
How to Reproduce: get a kingdom destroyed as an independent clan/ mercenary clan, then wait for a vassalage offer and the game will crash, without mods installed
How to Reproduce: get a kingdom destroyed as an independent clan/ mercenary clan, then wait for a vassalage offer and the game will crash, without mods installed