The game crashes. Log shows, that BtShowXp causes the issue.

[TaliesinWhite]

There is a exception from BtShowXp at the end of the log.

Crash log - output_log.txt

ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
at System.ThrowHelper.ThrowArgumentOutOfRangeException (System.ExceptionArgument argument, System.ExceptionResource resource) [0x00029] in :0
at System.ThrowHelper.ThrowArgumentOutOfRangeException () [0x00000] in :0
at BtShowXp.SkillXpCalc.GetXpCost (BattleTech.Pilot pilot) [0x00051] in :0
at BtShowXp.Patches.SetPilotXpText.Postfix (BattleTech.Pilot ___pilot, BattleTech.UI.TMProWrapper.LocalizableText ___callsign) [0x00005] in :0
at (wrapper dynamic-method) BattleTech.UI.SGBarracksRosterSlot.Refresh_Patch2(object)
at BattleTech.UI.SGBarracksRosterSlot.Init (BattleTech.Pilot p, BattleTech.UI.IMechLabDropTarget dropParent, UnityEngine.Events.UnityAction1[T0] onClick, System.Boolean setSelected, System.Boolean isDead) [0x00074] in <029bfe22d2d74c8e8c8ded1619022103>:0 at BattleTech.UI.SGBarracksRosterList.AddPilot (BattleTech.Pilot pilot, UnityEngine.Events.UnityAction1[T0] pilotSelectedOnClick, System.Boolean isInHireHall) [0x00038] in <029bfe22d2d74c8e8c8ded1619022103>:0
at BattleTech.UI.SGBarracksRosterList+<>c__DisplayClass46_0.b__0 () [0x00022] in <029bfe22d2d74c8e8c8ded1619022103>:0
at BattleTech.UI.SGBarracksRosterList+d__47.MoveNext () [0x0012e] in <029bfe22d2d74c8e8c8ded1619022103>:0
at UnityEngine.SetupCoroutine.InvokeMoveNext (System.Collections.IEnumerator enumerator, System.IntPtr returnValueAddress) [0x00027] in <9a6ceb7f013a4a599806f492fc789483>:0

[NBKRedSpy]

Can you give me your save and list of mods? It is most likely to be a mod incompatibility.

[TaliesinWhite]

Unfortunately, the save, where error occured, was overwritten, but I made a new save with the same mods enabled.
save&mods list.zip

The crash was on the 3rd mission of flashpoint "The Baying of Hounds" (variant 1, where you go with Kell). There are 2 allied mechs+pilots under your command in this mission. May be this triggers the bug.

I updated BTX_CAC. CAB & Hounfor`s TheBigDeal just before, so may be this is incompatibility with one of them. I suppose, it may be BTX_CAC, but not sure.

[NBKRedSpy]

I'm not sure if this will fix it, but can you try using the BEX specific version? It fixes a CAC-C compatibility issue.

https://github.com/NBKRedSpy/BtShowXp/releases/tag/1.3.2.0%2BBEX