The two mentioned mods are incompatible in a way that you are unable to increase and decrease the range of the arena spot.

This is the exact log that shows up when a placed arena spot is selected with this mod

Loading game from file with export agency with mods:
- brrainz.harmony
- Ludeon.RimWorld
- Ludeon.RimWorld.Royalty
- Cozarkian.WaterIsCold
- Mlie.PrisonerArena
- erdelf.ExportAgency
Verse.Log:Message(String, Boolean)
Verse.SavedGameLoaderNow:LoadGameFromSaveFileNow(String)
Verse.<>c:<Start>b__1_1()
Verse.LongEventHandler:RunEventFromAnotherThread(Action)
Verse.<>c:<UpdateCurrentAsynchronousEvent>b__27_0()
System.Threading.ThreadHelper:ThreadStart_Context(Object)
System.Threading.ExecutionContext:RunInternal(ExecutionContext, ContextCallback, Object, Boolean)
System.Threading.ExecutionContext:Run(ExecutionContext, ContextCallback, Object, Boolean)
System.Threading.ExecutionContext:Run(ExecutionContext, ContextCallback, Object)
System.Threading.ThreadHelper:ThreadStart()

System.NotImplementedException: The method or operation is not implemented.
at ArenaBell.Building_Bell.get_BillStack () [0x00001] in <1fd1ba7ec2494d4d9708ca5e5b0111ef>:0
at ExportAgency.ExportAgency.ExportGizmos (System.Object __instance, System.Collections.Generic.IEnumerable`1[Verse.Gizmo]& __result) [0x00029] in <d062aea3fff348cc8bdb8db812fed343>:0
at (wrapper dynamic-method) Verse.ThingWithComps.Verse.ThingWithComps.GetGizmos_Patch1(Verse.ThingWithComps)
at Verse.Building.<>n__0 () [0x00000] in <c36f9493c9844ddaa7fb5c788416098f>:0
at Verse.Building+<GetGizmos>d__18.MoveNext () [0x0003e] in <c36f9493c9844ddaa7fb5c788416098f>:0
at System.Collections.Generic.List`1[T].InsertRange (System.Int32 index, System.Collections.Generic.IEnumerable`1[T] collection) [0x000db] in <567df3e0919241ba98db88bec4c6696f>:0
at System.Collections.Generic.List`1[T].AddRange (System.Collections.Generic.IEnumerable`1[T] collection) [0x00000] in <567df3e0919241ba98db88bec4c6696f>:0
at RimWorld.InspectGizmoGrid.DrawInspectGizmoGridFor (System.Collections.Generic.IEnumerable`1[T] selectedObjects, Verse.Gizmo& mouseoverGizmo) [0x00045] in <c36f9493c9844ddaa7fb5c788416098f>:0
Verse.Log:Error(String, Boolean)
Verse.Log:ErrorOnce(String, Int32, Boolean)
RimWorld.InspectGizmoGrid:DrawInspectGizmoGridFor(IEnumerable`1, Gizmo&)
RimWorld.MainTabWindow_Inspect:DrawInspectGizmos()
RimWorld.InspectPaneUtility:ExtraOnGUI(IInspectPane)
RimWorld.MainTabWindow_Inspect:ExtraOnGUI()
Verse.WindowStack:WindowStackOnGUI()
RimWorld.UIRoot_Play:UIRootOnGUI()
Verse.Root:OnGUI()