Continuation... Been really trying to locate the issue because I've replicated it on 5 different playthroughs, usually happens pretty early on in the game. I thought it was realistic battle mod or serve as soldier at first but it would keep happening after disabled those mods. Its a game-breaking crash so I downloaded Better Exception Window mod to show callstacks and this is what it showed.
Source: TaleWorlds.CampaignSystem
Object reference not set to an instance of an object.
Outer exception callstack: at TaleWorlds.CampaignSystem.GameComponents.DefaultArmyManagementCalculationModel.CalculatePartyInfluenceCost(MobileParty armyLeaderParty, MobileParty party)
at TaleWorlds.CampaignSystem.GameComponents.DefaultArmyManagementCalculationModel.GetMobilePartiesToCallToArmy(MobileParty leaderParty)
at TaleWorlds.CampaignSystem.CampaignBehaviors.AiBehaviors.AiMilitaryBehavior.AiHourlyTick(MobileParty mobileParty, PartyThinkParams p)
at TaleWorlds.CampaignSystem.MbEvent`2.InvokeList(EventHandlerRec`2 list, T1 t1, T2 t2)
at TaleWorlds.CampaignSystem.CampaignEvents.AiHourlyTick(MobileParty party, PartyThinkParams partyThinkParams)
at TaleWorlds.CampaignSystem.CampaignEventDispatcher.AiHourlyTick(MobileParty party, PartyThinkParams partyThinkParams)
at TaleWorlds.CampaignSystem.CampaignBehaviors.AiBehaviors.AiPartyThinkBehavior.PartyHourlyAiTick(MobileParty mobileParty)
at TaleWorlds.CampaignSystem.MbEvent`1.InvokeList(EventHandlerRec`1 list, T t)
at TaleWorlds.CampaignSystem.CampaignEvents.TickPartialHourlyAi(MobileParty party)
at TaleWorlds.CampaignSystem.CampaignEventDispatcher.TickPartialHourlyAi(MobileParty party)
at TaleWorlds.CampaignSystem.CampaignPeriodicEventManager.PeriodicTicker`1.PeriodicTickSome(Double timeUnitsElapsed)
at TaleWorlds.CampaignSystem.CampaignPeriodicEventManager.TickPartialHourlyAi()
at TaleWorlds.CampaignSystem.Campaign.Tick()
at TaleWorlds.CampaignSystem.GameState.MapState.OnMapModeTick(Single dt)
at TaleWorlds.CampaignSystem.GameState.MapState.OnTick(Single dt)
at TaleWorlds.Core.GameStateManager.OnTick(Single dt)
at TaleWorlds.Core.Game.OnTick(Single dt)
at TaleWorlds.Core.GameManagerBase.OnTick(Single dt)
at TaleWorlds.MountAndBlade.Module.OnApplicationTick_Patch1(Module this, Single dt)
I have almost 900 hours on this game and it was driving me crazy. Hope this helps, if not maybe there's further details I can show.