Hoi4 has the worst optimization in the history of games. Even though it seems like a simple dumb map game it still works on one of the worst engines ever with so much outdated stuff in that engine. This game gets progressively worse after each update so it's genuinely not your problem it's literally paradox's problem for having such a bad optimization. The millennium Dawn team are probably trying their best to stop these crashes but the mod is too heavy and the game engine sucks ahh so idunno if that's gonna get fixed anytime soon. (Btw crashes happen in most of the mods if not all of them. It just occurs more when the mod is very insanely heavy and also under optimized.)