Error at creation 'ArgumentException: Getting control 2's position in a group with only 2 controls when doing repaint'

[mitay-walle]

Stacktrace:

ArgumentException: Getting control 2's position in a group with only 2 controls when doing repaint
Aborting
UnityEngine.GUILayoutGroup.GetNext () 
UnityEngine.GUILayoutUtility.DoGetRect (UnityEngine.GUIContent content, UnityEngine.GUIStyle style, UnityEngine.GUILayoutOption[] options)
UnityEngine.GUILayoutUtility.GetRect (UnityEngine.GUIContent content, UnityEngine.GUIStyle style, UnityEngine.GUILayoutOption[] options)
UnityEditor.EditorGUILayout.DropdownButton (UnityEngine.GUIContent content, UnityEngine.FocusType focusType, UnityEngine.GUIStyle style, UnityEngine.GUILayoutOption[] options)
UnityEditor.InspectorWindow.EndDrawPreviewAndLabels (UnityEngine.Event evt, UnityEngine.Rect rect, UnityEngine.Rect dragRect)
UnityEditor.PropertyEditor.DrawPreviewAndLabels () 
UnityEngine.UIElements.IMGUIContainer.DoOnGUI (UnityEngine.Event evt, UnityEngine.Matrix4x4 parentTransform, UnityEngine.Rect clippingRect, System.Boolean isComputingLayout, UnityEngine.Rect layoutSize, System.Action onGUIHandler, System.Boolean canAffectFocus) 
UnityEngine.UIElements.IMGUIContainer.HandleIMGUIEvent (UnityEngine.Event e, UnityEngine.Matrix4x4 worldTransform, UnityEngine.Rect clippingRect, System.Action onGUIHandler, System.Boolean canAffectFocus)
UnityEngine.UIElements.IMGUIContainer.DoIMGUIRepaint ()
UnityEngine.UIElements.UIR.RenderChainCommand.ExecuteNonDrawMesh (UnityEngine.UIElements.UIR.DrawParams drawParams, System.Single pixelsPerPoint, System.Exception& immediateException)
Rethrow as ImmediateModeException
UnityEngine.UIElements.UIR.RenderChain.Render ()
UnityEngine.UIElements.UIRRepaintUpdater.Update ()
UnityEngine.UIElements.VisualTreeUpdater.UpdateVisualTreePhase (UnityEngine.UIElements.VisualTreeUpdatePhase phase) 
UnityEngine.UIElements.Panel.UpdateForRepaint ()
UnityEngine.UIElements.Panel.Repaint (UnityEngine.Event e)
UnityEngine.UIElements.UIElementsUtility.DoDispatch (UnityEngine.UIElements.BaseVisualElementPanel panel) 
UnityEngine.UIElements.UIElementsUtility.UnityEngine.UIElements.IUIElementsUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr, System.Boolean& eventHandled)
UnityEngine.UIElements.UIEventRegistration.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr) 
UnityEngine.UIElements.UIEventRegistration+<>c.<.cctor>b__1_2 (System.Int32 i, System.IntPtr ptr)
UnityEngine.GUIUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr, System.Boolean& result)