1. Go to default layout.
2. Move inspector or project browser windows somewhere. Doesn't always happen, but pretty frequent.
(it should reproduce in less than 10 docking attempts)

Errors in console

Reproduced on:
Version: 2020.2.0a1 trunk -- 2edf46a36d00

unique_ptr move assignment error. rhs memory label does not match.
UnityEngine.StackTraceUtility:ExtractStackTrace () (at C:/unity/Runtime/Export/Scripting/StackTrace.cs:37)
UnityEditor.SavedGUIState:Create () (at C:/unity/Editor/Mono/SavedGUIState.bindings.cs:40)
UnityEditor.SplitView:SetupRectsFromSplitter () (at C:/unity/Editor/Mono/GUI/SplitView.cs:103)
UnityEditor.SplitView:Reflow () (at C:/unity/Editor/Mono/GUI/SplitView.cs:156)
UnityEditor.DockArea:AddTab (int,UnityEditor.EditorWindow,bool) (at C:/unity/Editor/Mono/GUI/DockArea.cs:181)
UnityEditor.DockArea:AddTab (UnityEditor.EditorWindow,bool) (at C:/unity/Editor/Mono/GUI/DockArea.cs:169)
UnityEditor.SplitView:PerformDrop (UnityEditor.EditorWindow,UnityEditor.DropInfo,UnityEngine.Vector2) (at C:/unity/Editor/Mono/GUI/SplitView.cs:452)
UnityEditor.DockArea:DragTab (UnityEngine.Rect,single,UnityEngine.GUIStyle,UnityEngine.GUIStyle) (at C:/unity/Editor/Mono/GUI/DockArea.cs:905)
UnityEditor.DockArea:DrawTabs (UnityEngine.Rect) (at C:/unity/Editor/Mono/GUI/DockArea.cs:384)
UnityEditor.DockArea:OldOnGUI () (at C:/unity/Editor/Mono/GUI/DockArea.cs:351)
UnityEngine.UIElements.IMGUIContainer:DoOnGUI (UnityEngine.Event,UnityEngine.Matrix4x4,UnityEngine.Rect,bool,UnityEngine.Rect,System.Action,bool) (at C:/unity/Modules/UIElements/IMGUIContainer.cs:294)
UnityEngine.UIElements.IMGUIContainer:HandleIMGUIEvent (UnityEngine.Event,UnityEngine.Matrix4x4,UnityEngine.Rect,System.Action,bool) (at C:/unity/Modules/UIElements/IMGUIContainer.cs:618)
UnityEngine.UIElements.IMGUIContainer:HandleIMGUIEvent (UnityEngine.Event,System.Action,bool) (at C:/unity/Modules/UIElements/IMGUIContainer.cs:590)
UnityEngine.UIElements.IMGUIContainer:HandleIMGUIEvent (UnityEngine.Event,bool) (at C:/unity/Modules/UIElements/IMGUIContainer.cs:583)
UnityEngine.UIElements.IMGUIContainer:SendEventToIMGUIRaw (UnityEngine.UIElements.EventBase,bool,bool) (at C:/unity/Modules/UIElements/IMGUIContainer.cs:549)
UnityEngine.UIElements.IMGUIContainer:SendEventToIMGUI (UnityEngine.UIElements.EventBase,bool,bool) (at C:/unity/Modules/UIElements/IMGUIContainer.cs:538)
UnityEngine.UIElements.IMGUIContainer:HandleEvent (UnityEngine.UIElements.EventBase) (at C:/unity/Modules/UIElements/IMGUIContainer.cs:471)
UnityEngine.UIElements.CallbackEventHandler:HandleEventAtTargetPhase (UnityEngine.UIElements.EventBase) (at C:/unity/Modules/UIElements/Events/EventHandler.cs:77)
UnityEngine.UIElements.MouseCaptureDispatchingStrategy:DispatchEvent (UnityEngine.UIElements.EventBase,UnityEngine.UIElements.IPanel) (at C:/unity/Modules/UIElements/Events/MouseCaptureDispatchingStrategy.cs:92)
UnityEngine.UIElements.EventDispatcher:ApplyDispatchingStrategies (UnityEngine.UIElements.EventBase,UnityEngine.UIElements.IPanel,bool) (at C:/unity/Modules/UIElements/EventDispatcher.cs:318)
UnityEngine.UIElements.EventDispatcher:ProcessEvent (UnityEngine.UIElements.EventBase,UnityEngine.UIElements.IPanel) (at C:/unity/Modules/UIElements/EventDispatcher.cs:281)
UnityEngine.UIElements.EventDispatcher:ProcessEventQueue () (at C:/unity/Modules/UIElements/EventDispatcher.cs:244)
UnityEngine.UIElements.EventDispatcher:OpenGate () (at C:/unity/Modules/UIElements/EventDispatcher.cs:209)
UnityEngine.UIElements.EventDispatcherGate:Dispose () (at C:/unity/Modules/UIElements/EventDispatcher.cs:44)
UnityEngine.UIElements.EventDispatcher:ProcessEvent (UnityEngine.UIElements.EventBase,UnityEngine.UIElements.IPanel) (at C:/unity/Modules/UIElements/EventDispatcher.cs:309)
UnityEngine.UIElements.EventDispatcher:Dispatch (UnityEngine.UIElements.EventBase,UnityEngine.UIElements.IPanel,UnityEngine.UIElements.DispatchMode) (at C:/unity/Modules/UIElements/EventDispatcher.cs:161)
UnityEngine.UIElements.BaseVisualElementPanel:SendEvent (UnityEngine.UIElements.EventBase,UnityEngine.UIElements.DispatchMode) (at C:/unity/Modules/UIElements/Panel.cs:277)
UnityEngine.UIElements.UIElementsUtility:DoDispatch (UnityEngine.UIElements.BaseVisualElementPanel) (at C:/unity/Modules/UIElements/UIElementsUtility.cs:459)
UnityEngine.UIElements.UIElementsUtility:UnityEngine.UIElements.IUIElementsUtility.ProcessEvent (int,intptr,bool&) (at C:/unity/Modules/UIElements/UIElementsUtility.cs:209)
UnityEngine.UIElements.UIEventRegistration:ProcessEvent (int,intptr) (at C:/unity/Modules/UIElements/UIElementsUtility.cs:74)
UnityEngine.UIElements.UIEventRegistration/<>c:<.cctor>b__1_2 (int,intptr) (at C:/unity/Modules/UIElements/UIElementsUtility.cs:28)
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&) (at C:/unity/Modules/IMGUI/GUIUtility.cs:180)
[C:/unity/Runtime/Export/Scripting/StackTrace.cs line 37]