Behavior Tree Lost when editing in Prefab Mode. 2018.3

2018.3

I get this error everytime I want to edit more than prefabs on 2018.3
I nave tried on Mac and Windows.
I always get this error (below) and the tree dissapears (gets empty screen).

So basically if you work just with 1 prefab / tree everything works fine as I mentioned here:
https://opsive.com/forum/index.php?threads/possible-bug-view-only-mode.670/#post-3317

But as long as you try to have more than one agent (prefabs), even with the same tree, crashes.
I have tried more than 20 times right now in different combinations.

EDIT: I have tried to assign a external tree (exporting first the actual tree and assigning on the component) with the same result.

InvalidCastException: Specified cast is not valid.
BinaryDeserialization.BytesToSharedVariable (BehaviorDesigner.Runtime.FieldSerializationData fieldSerializationData, System.Collections.Generic.Dictionary`2[TKey,TValue] fieldIndexMap, System.Byte[] bytes, System.Int32 dataPosition, BehaviorDesigner.Runtime.IVariableSource variableSource, System.Boolean fromField, System.Int32 hashPrefix) (at <9fd26eacf1af4bd8ab9b56956877bd65>:0)
BinaryDeserialization.Load (BehaviorDesigner.Runtime.TaskSerializationData taskData, BehaviorDesigner.Runtime.BehaviorSource behaviorSource) (at <9fd26eacf1af4bd8ab9b56956877bd65>:0)
BehaviorDesigner.Runtime.BehaviorSource.CheckForSerialization (System.Boolean force, BehaviorDesigner.Runtime.BehaviorSource behaviorSource) (at <9fd26eacf1af4bd8ab9b56956877bd65>:0)
BehaviorDesigner.Editor.GraphDesigner.Load (BehaviorDesigner.Runtime.BehaviorSource behaviorSource, System.Boolean loadPrevBehavior, UnityEngine.Vector2 nodePosition) (at <6224ec08a63b4190a0704159812b1ad4>:0)
BehaviorDesigner.Editor.BehaviorDesignerWindow.LoadBehavior (BehaviorDesigner.Runtime.BehaviorSource behaviorSource, System.Boolean loadPrevBehavior, System.Boolean inspectorLoad) (at <6224ec08a63b4190a0704159812b1ad4>:0)
BehaviorDesigner.Editor.BehaviorInspector.DrawInspectorGUI (BehaviorDesigner.Runtime.Behavior behavior, UnityEditor.SerializedObject serializedObject, System.Boolean fromInspector, System.Boolean& externalModification, System.Boolean& showOptions, System.Boolean& showVariables) (at <6224ec08a63b4190a0704159812b1ad4>:0)
BehaviorDesigner.Editor.BehaviorInspector.OnInspectorGUI () (at <6224ec08a63b4190a0704159812b1ad4>:0)
UnityEditor.InspectorWindow.DoOnInspectorGUI (System.Boolean rebuildOptimizedGUIBlock, UnityEditor.Editor editor, System.Boolean wasVisible, UnityEngine.Rect& contentRect) (at C:/buildslave/unity/build/Editor/Mono/Inspector/InspectorWindow.cs:1625)
UnityEngine.GUIUtility:processEvent(Int32, IntPtr)
 
Top