Not sure if it's the same thing, but I had a pawn go to fire, then instead of firing their ammo went to zero and they started reloading instead:

Root level exception in OnGUI(): System.IndexOutOfRangeException: Index was outside the bounds of the array.
at Verse.RoofGrid.Roofed (Verse.IntVec3 c) [0x00017] in <1b9c4c73530448bcbb33283e1d4d7d05>:0
at (wrapper dynamic-method) Verse.GlowGrid.Verse.GlowGrid.GameGlowAt_Patch1(Verse.GlowGrid,Verse.IntVec3,bool)
at CombatExtended.LightingTracker.CombatGlowAtFor (Verse.IntVec3 source, Verse.IntVec3 target) [0x00001] in <ccb6738ca9da4e0ba4122c09aec10cab>:0
at CombatExtended.Verb_LaunchProjectileCE.ShiftVecReportFor (Verse.LocalTargetInfo target) [0x00077] in <ccb6738ca9da4e0ba4122c09aec10cab>:0
at CombatExtended.HarmonyCE.Harmony_TooltipUtility_ShotCalculationTipString_Patch.Postfix (System.String& __result, Verse.Thing target) [0x0011d] in <ccb6738ca9da4e0ba4122c09aec10cab>:0
at (wrapper dynamic-method) Verse.TooltipUtility.Verse.TooltipUtility.ShotCalculationTipString_Patch1(Verse.Thing)
at Verse.TooltipGiverList.DispenseAllThingTooltips () [0x0012a] in <1b9c4c73530448bcbb33283e1d4d7d05>:0
at (wrapper dynamic-method) RimWorld.MapInterface.RimWorld.MapInterface.MapInterfaceOnGUI_BeforeMainTabs_Patch1(RimWorld.MapInterface)
at RimWorld.UIRoot_Play.UIRootOnGUI () [0x0001f] in <1b9c4c73530448bcbb33283e1d4d7d05>:0
at (wrapper dynamic-method) Verse.Root.Verse.Root.OnGUI_Patch1(Verse.Root)
(Filename: C:\buildslave\unity\build\Runtime/Export/Debug/Debug.bindings.h Line: 39)

https://gist.github.com/HugsLibRecordKeeper/463568f61c9b0e65e61b620d80b9c8f5

Bug fixed recently! Expect the next version to work without error.

If you encounter the bug, save/reload your game - it has to do with a caching error.