I don't know how to interpret the details, but Visual Exceptions and the default debug screen are reporting an interaction between this and Humanoid Alien Races when generating starting pawns.

Exception filling window for RimWorld.Page_ConfigureStartingPawns: System.NullReferenceException: Object reference not set to an instance of an object
[Ref E871904D]
at Verse.PawnGenerationRequest.AlwaysDownedLifeStages (System.String& stages) [0x00020] in <fcfab19af5d14a608a65ebd77f29482f>:0
at Verse.PawnGenerationRequest.ValidateAndFix () [0x0008e] in <fcfab19af5d14a608a65ebd77f29482f>:0
<0x2867c2eb710 + 0x007e2> <unknown method>
at Verse.StartingPawnUtility.get_DefaultStartingPawnRequest () [0x0007a] in <fcfab19af5d14a608a65ebd77f29482f>:0
- TRANSPILER rimworld.erdelf.alien_race.main: IEnumerable`1 AlienRace.HarmonyPatches:DefaultStartingPawnTranspiler(IEnumerable`1 instructions, ILGenerator ilg)
at Verse.StartingPawnUtility.EnsureGenerationRequestInRangeOf (System.Int32 index) [0x00002] in <fcfab19af5d14a608a65ebd77f29482f>:0
at Verse.StartingPawnUtility.GetGenerationRequest (System.Int32 index) [0x00000] in <fcfab19af5d14a608a65ebd77f29482f>:0
at RimWorld.CharacterCardUtility+<>c__DisplayClass36_0.<LifestageAndXenotypeOptions>g__GetDevelopmentalStageIcon|1 () [0x00000] in <fcfab19af5d14a608a65ebd77f29482f>:0
at RimWorld.CharacterCardUtility.LifestageAndXenotypeOptions (Verse.Pawn pawn, UnityEngine.Rect randomizeRect, System.Boolean creationMode, System.Boolean allowsChildSelection, System.Action randomizeCallback) [0x001f2] in <fcfab19af5d14a608a65ebd77f29482f>:0
- TRANSPILER rimworld.erdelf.alien_race.main: IEnumerable`1 AlienRace.HarmonyPatches:LifestageAndXenotypeOptionsTranspiler(IEnumerable`1 instructions)
- TRANSPILER Altered.Carbon: IEnumerable`1 AlteredCarbon.CharacterCardUtility_LifestageAndXenotypeOptions_Patch:Transpiler(IEnumerable`1 codeInstructions)
at RimWorld.CharacterCardUtility.DrawCharacterCard (UnityEngine.Rect rect, Verse.Pawn pawn, System.Action randomizeCallback, UnityEngine.Rect creationRect, System.Boolean showName) [0x00378] in <fcfab19af5d14a608a65ebd77f29482f>:0
- TRANSPILER VFEEmpire.Mod: IEnumerable`1 VFEEmpire.HarmonyPatches.Patch_StripTitles:Transpiler(IEnumerable`1 instructions)
- TRANSPILER vanillaexpanded.skills: IEnumerable`1 VSE.Expertise.ExpertisePatches:CharacterCardTranspiler(IEnumerable`1 instructions, ILGenerator generator)
- TRANSPILER rimworld.erdelf.alien_race.main: IEnumerable`1 AlienRace.HarmonyPatches:DrawCharacterCardTranspiler(IEnumerable`1 instructions)
- TRANSPILER Altered.Carbon: IEnumerable`1 AlteredCarbon.CharacterCardUtility_DrawCharacterCard_Patch:Transpiler(IEnumerable`1 codeInstructions)
at Verse.StartingPawnUtility.DrawPortraitArea (UnityEngine.Rect rect, System.Int32 pawnIndex, System.Boolean renderClothes, System.Boolean renderHeadgear) [0x000ca] in <fcfab19af5d14a608a65ebd77f29482f>:0
at RimWorld.Page_ConfigureStartingPawns.DoWindowContents (UnityEngine.Rect rect) [0x001e5] in <fcfab19af5d14a608a65ebd77f29482f>:0
at Verse.Window.InnerWindowOnGUI (System.Int32 x) [0x001d3] in <fcfab19af5d14a608a65ebd77f29482f>:0
- TRANSPILER net.pardeike.rimworld.lib.harmony: IEnumerable`1 VisualExceptions.ExceptionsAndActivatorHandler:Transpiler(IEnumerable`1 instructions, MethodBase original)
UnityEngine.StackTraceUtility:ExtractStackTrace ()
(wrapper dynamic-method) MonoMod.Utils.DynamicMethodDefinition:Verse.Log.Error_Patch1 (string)
(wrapper dynamic-method) MonoMod.Utils.DynamicMethodDefinition:Verse.Window.InnerWindowOnGUI_Patch0 (Verse.Window,int)
UnityEngine.GUI:CallWindowDelegate (UnityEngine.GUI/WindowFunction,int,int,UnityEngine.GUISkin,int,single,single,UnityEngine.GUIStyle)