Unfortunately I didn't save the crash logs and now of course I can't seem to repeat the crash since I have already rebuilt the missing tree and I'm also now on 2018.3.11 but it initially got corrupted while on 2018.3.9.
I guess something corrupted the prefab component but I'm not sure what.
I've attached the corrupted prefab incase it's helpful. If I import it in a new project it throws these errors in the console:
ArgumentOutOfRangeException: ArgRange_Array
Parameter name: count
System.Text.UTF8Encoding.InternalGetCharCount (System.Byte[] bytes, Int32 index, Int32 count, UInt32 leftOverBits, UInt32 leftOverCount, System.Object provider, System.Text.DecoderFallbackBuffer& fallbackBuffer, System.Byte[]& bufferArg, Boolean flush) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Text/UTF8Encoding.cs:462)
System.Text.UTF8Encoding.GetCharCount (System.Byte[] bytes, Int32 index, Int32 count) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Text/UTF8Encoding.cs:687)
System.Text.Encoding.GetChars (System.Byte[] bytes, Int32 index, Int32 count) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Text/Encoding.cs:328)
System.Text.Encoding.GetString (System.Byte[] bytes, Int32 index, Int32 count) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Text/Encoding.cs:751)
System.Text.UTF8Encoding.GetString (System.Byte[] bytes, Int32 index, Int32 count) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Text/UTF8Encoding.cs:1052)
BinaryDeserialization.BytesToString (System.Byte[] bytes, Int32 dataPosition, Int32 dataSize)
BinaryDeserialization.LoadField (BehaviorDesigner.Runtime.FieldSerializationData fieldSerializationData, System.Collections.Generic.Dictionary`2 fieldIndexMap, System.Type fieldType, System.String fieldName, Int32 hashPrefix, IVariableSource variableSource, System.Object obj, System.Reflection.FieldInfo fieldInfo)
BinaryDeserialization.BytesToSharedVariable (BehaviorDesigner.Runtime.FieldSerializationData fieldSerializationData, System.Collections.Generic.Dictionary`2 fieldIndexMap, System.Byte[] bytes, Int32 dataPosition, IVariableSource variableSource, Boolean fromField, Int32 hashPrefix)
BinaryDeserialization.LoadField (BehaviorDesigner.Runtime.FieldSerializationData fieldSerializationData, System.Collections.Generic.Dictionary`2 fieldIndexMap, System.Type fieldType, System.String fieldName, Int32 hashPrefix, IVariableSource variableSource, System.Object obj, System.Reflection.FieldInfo fieldInfo)
BinaryDeserialization.LoadFields (BehaviorDesigner.Runtime.FieldSerializationData fieldSerializationData, System.Collections.Generic.Dictionary`2 fieldIndexMap, System.Object obj, Int32 hashPrefix, IVariableSource variableSource)
BinaryDeserialization.LoadTask (BehaviorDesigner.Runtime.TaskSerializationData taskSerializationData, BehaviorDesigner.Runtime.FieldSerializationData fieldSerializationData, System.Collections.Generic.List`1& taskList, BehaviorDesigner.Runtime.BehaviorSource& behaviorSource)
BinaryDeserialization.Load (BehaviorDesigner.Runtime.TaskSerializationData taskData, BehaviorDesigner.Runtime.BehaviorSource behaviorSource)
BehaviorDesigner.Runtime.BehaviorSource.CheckForSerialization (Boolean force, BehaviorDesigner.Runtime.BehaviorSource behaviorSource)
BehaviorDesigner.Editor.GraphDesigner.Load (BehaviorDesigner.Runtime.BehaviorSource behaviorSource, Boolean loadPrevBehavior, Vector2 nodePosition)
BehaviorDesigner.Editor.BehaviorDesignerWindow.LoadBehavior (BehaviorDesigner.Runtime.BehaviorSource behaviorSource, Boolean loadPrevBehavior, Boolean inspectorLoad)
BehaviorDesigner.Editor.BehaviorDesignerWindow.UpdateTree (Boolean firstLoad)
BehaviorDesigner.Editor.BehaviorDesignerWindow.OnSelectionChange ()
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:232)
System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MethodBase.cs:115)
UnityEditor.HostView.Invoke (System.String methodName, System.Object obj) (at /Users/builduser/buildslave/unity/build/Editor/Mono/HostView.cs:342)
UnityEditor.HostView.Invoke (System.String methodName) (at /Users/builduser/buildslave/unity/build/Editor/Mono/HostView.cs:336)
UnityEditor.HostView.OnSelectionChange () (at /Users/builduser/buildslave/unity/build/Editor/Mono/HostView.cs:199)