Make sure you download the latest package and then run the installer.
That should fix this issue.
Alternatively, Unity just released 6000.3.5f1 that fixes this bug, so updating Unity should also fix the issue now.
GUI Error: Invalid GUILayout state in FsmEditorWindow view. Verify that all layout Begin/End calls match
0x00007ffe831217ae (Unity) StackWalker::ShowCallstack
0x00007ffe84952da9 (Unity) PlatformStacktrace::GetStacktrace
0x00007ffe8495362e (Unity) Stacktrace::GetStacktrace
0x00007ffe830d220f (Unity) DebugStringToFile
0x00007ffe82f8a7b0 (Unity) DebugLogHandler_CUSTOM_Internal_Log
0x000002020e6106ad (Mono JIT Code) (wrapper managed-to-native) UnityEngine.DebugLogHandler:Internal_Log_Injected (UnityEngine.LogType,UnityEngine.LogOption,UnityEngine.Bindings.ManagedSpanWrapper&,intptr)
0x000002020e610563 (Mono JIT Code) UnityEngine.DebugLogHandler:Internal_Log (UnityEngine.LogType,UnityEngine.LogOption,string,UnityEngine.Object)
0x000002020e61017b (Mono JIT Code) UnityEngine.DebugLogHandler:LogFormat (UnityEngine.LogType,UnityEngine.Object,string,object[])
0x000002020e60fea0 (Mono JIT Code) UnityEngine.Logger:Log (UnityEngine.LogType,object)
0x000002020e60fd65 (Mono JIT Code) UnityEngine.Debug:LogError (object)
0x000002017e9b08cb (Mono JIT Code) UnityEditor.HostView:InvokeOnGUI (UnityEngine.Rect)
0x000002017e9b0353 (Mono JIT Code) UnityEditor.DockArea:DrawView (UnityEngine.Rect)
0x000002017e86e55b (Mono JIT Code) UnityEditor.DockArea:OldOnGUI ()
0x000002017d8099af (Mono JIT Code) UnityEngine.UIElements.IMGUIContainer:DoOnGUI (UnityEngine.Event,UnityEngine.Matrix4x4,UnityEngine.Rect,bool,UnityEngine.Rect,System.Action,bool)
0x000002017d8087ab (Mono JIT Code) UnityEngine.UIElements.IMGUIContainer:HandleIMGUIEvent (UnityEngine.Event,UnityEngine.Matrix4x4,UnityEngine.Rect,System.Action,bool)
0x000001ffbe7e56bb (Mono JIT Code) UnityEngine.UIElements.IMGUIContainer:HandleIMGUIEvent (UnityEngine.Event,System.Action,bool)
0x000001ffbe7ee493 (Mono JIT Code) UnityEngine.UIElements.IMGUIContainer:HandleIMGUIEvent (UnityEngine.Event,bool)
0x000001ffbe7ede2b (Mono JIT Code) UnityEngine.UIElements.IMGUIContainer:SendEventToIMGUIRaw (UnityEngine.UIElements.EventBase,bool,bool)
0x000001ffbe7edd13 (Mono JIT Code) UnityEngine.UIElements.IMGUIContainer:SendEventToIMGUI (UnityEngine.UIElements.EventBase,bool,bool)
0x00000201330086c3 (Mono JIT Code) UnityEngine.UIElements.IMGUIContainer:HandleEventBubbleUp (UnityEngine.UIElements.EventBase)
0x000001ffbe7e421e (Mono JIT Code) UnityEngine.UIElements.EventDispatchUtilities:HandleEventAcrossPropagationPathWithCompatibilityEvent (UnityEngine.UIElements.EventBase,UnityEngine.UIElements.EventBase,UnityEngine.UIElements.BaseVisualElementPanel,UnityEngine.UIElements.VisualElement,bool)
0x000001ffbe7e2e1b (Mono JIT Code) UnityEngine.UIElements.EventDispatchUtilities:DispatchToElementUnderPointerOrPanelRoot (UnityEngine.UIElements.EventBase,UnityEngine.UIElements.BaseVisualElementPanel,int,UnityEngine.Vector2)
0x000001ffbe7e2a73 (Mono JIT Code) UnityEngine.UIElements.EventDispatchUtilities:DispatchToCapturingElementOrElementUnderPointer (UnityEngine.UIElements.EventBase,UnityEngine.UIElements.BaseVisualElementPanel,int,UnityEngine.Vector2)
0x000001ffbe7e254b (Mono JIT Code) UnityEngine.UIElements.PointerMoveEvent:Dispatch (UnityEngine.UIElements.BaseVisualElementPanel)
0x00000201340cfdae (Mono JIT Code) UnityEngine.UIElements.EventDispatcher:ProcessEvent (UnityEngine.UIElements.EventBase,UnityEngine.UIElements.BaseVisualElementPanel)
0x00000201340cd673 (Mono JIT Code) UnityEngine.UIElements.EventDispatcher:Dispatch (UnityEngine.UIElements.EventBase,UnityEngine.UIElements.BaseVisualElementPanel,UnityEngine.UIElements.DispatchMode)
0x00000201340cd413 (Mono JIT Code) UnityEngine.UIElements.BaseVisualElementPanel:SendEvent (UnityEngine.UIElements.EventBase,UnityEngine.UIElements.DispatchMode)
0x00000201352235db (Mono JIT Code) UnityEngine.UIElements.UIElementsUtility:DoDispatch (UnityEngine.UIElements.BaseVisualElementPanel)
0x0000020135222f8b (Mono JIT Code) UnityEngine.UIElements.UIElementsUtility:UnityEngine.UIElements.IUIElementsUtility.ProcessEvent (int,intptr,bool&)
0x0000020135222cef (Mono JIT Code) UnityEngine.UIElements.UIEventRegistration:ProcessEvent (int,intptr)
0x0000020135222c0b (Mono JIT Code) UnityEngine.UIElements.UIEventRegistration/<>c:<.cctor>b__1_2 (int,intptr)
0x0000020135221b2a (Mono JIT Code) UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)
0x0000020135221ce6 (Mono JIT Code) (wrapper runtime-invoke) <Module>:runtime_invoke_void_int_intptr_intptr& (object,intptr,intptr,intptr)
0x00007ffe7aec6bfe (mono-2.0-bdwgc) mono_jit_runtime_invoke (at C:/build/output/Unity-Technologies/mono/mono/mini/mini-runtime.c:3445)
0x00007ffe7ae08984 (mono-2.0-bdwgc) do_runtime_invoke (at C:/build/output/Unity-Technologies/mono/mono/metadata/object.c:3068)
0x00007ffe7ae08a70 (mono-2.0-bdwgc) mono_runtime_invoke (at C:/build/output/Unity-Technologies/mono/mono/metadata/object.c:3115)
0x00007ffe839571e4 (Unity) scripting_method_invoke
0x00007ffe8395e0a3 (Unity) ScriptingInvocation::Invoke
0x00007ffe83959645 (Unity) ScriptingInvocation::Invoke<void>
0x00007ffe848ea6ed (Unity) Scripting::UnityEngine::GUIUtilityProxy::ProcessEvent
0x00007ffe846ab3f4 (Unity) GUIView::ProcessRetainedMode
0x00007ffe83fb1f69 (Unity) GUIView::OnInputEvent
0x00007ffe846ab2cd (Unity) GUIView::ProcessInputEvent
0x00007ffe83fb2d0a (Unity) GUIViewPlatform::ProcessEventMessages
0x00007ffe83faf60c (Unity) GUIViewPlatform::GUIViewWndProc
0x00007ffee280ef5c (USER32) CallWindowProcW
0x00007ffee280e684 (USER32) DispatchMessageW
0x00007ffe83f72755 (Unity) MainMessageLoop
0x00007ffe83f7a262 (Unity) UnityMain
0x00007ff6357e2f2a (Unity) __scrt_common_main_seh
0x00007ffee3557374 (KERNEL32) BaseThreadInitThunk
0x00007ffee369cc91 (ntdll) RtlUserThreadStart
TypeLoadException: Could not resolve type with token 01000186 from typeref (expected class 'UnityEngine.EventModifiers' in assembly 'UnityEngine.CoreModule, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null')
HutongGames.PlayMakerEditor.CanvasView.HandleInputEvents () (at <afd01bdcac7848349e9af97d038deec7>:0)
HutongGames.PlayMakerEditor.CanvasView.BeginGUILayout (UnityEngine.Rect view, System.Boolean showScrollBars) (at <afd01bdcac7848349e9af97d038deec7>:0)
HutongGames.PlayMakerEditor.FsmGraphView.DoCanvasView () (at <afd01bdcac7848349e9af97d038deec7>:0)
HutongGames.PlayMakerEditor.FsmGraphView.OnGUI (UnityEngine.Rect area) (at <afd01bdcac7848349e9af97d038deec7>:0)
HutongGames.PlayMakerEditor.FsmEditor.OnGUI () (at <afd01bdcac7848349e9af97d038deec7>:0)
HutongGames.PlayMakerEditor.FsmEditorWindow.DoGUI () (at Assets/PlayMaker/Editor/FsmEditorWindow.cs:214)
HutongGames.PlayMakerEditor.BaseEditorWindow.OnGUI () (at <afd01bdcac7848349e9af97d038deec7>:0)
UnityEditor.HostView.InvokeOnGUI (UnityEngine.Rect onGUIPosition) (at <0b7b383646aa48089bb2b1f124c725a3>:0)
UnityEditor.DockArea.DrawView (UnityEngine.Rect dockAreaRect) (at <0b7b383646aa48089bb2b1f124c725a3>:0)
UnityEditor.DockArea.OldOnGUI () (at <0b7b383646aa48089bb2b1f124c725a3>:0)
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) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.IMGUIContainer.HandleIMGUIEvent (UnityEngine.Event e, UnityEngine.Matrix4x4 worldTransform, UnityEngine.Rect clippingRect, System.Action onGUIHandler, System.Boolean canAffectFocus) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.IMGUIContainer.HandleIMGUIEvent (UnityEngine.Event e, System.Action onGUIHandler, System.Boolean canAffectFocus) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.IMGUIContainer.HandleIMGUIEvent (UnityEngine.Event e, System.Boolean canAffectFocus) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.IMGUIContainer.SendEventToIMGUIRaw (UnityEngine.UIElements.EventBase evt, System.Boolean canAffectFocus, System.Boolean verifyBounds) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.IMGUIContainer.SendEventToIMGUI (UnityEngine.UIElements.EventBase evt, System.Boolean canAffectFocus, System.Boolean verifyBounds) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.IMGUIContainer.HandleEventBubbleUp (UnityEngine.UIElements.EventBase evt) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.EventDispatchUtilities.HandleEventAcrossPropagationPathWithCompatibilityEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.EventBase compatibilityEvt, UnityEngine.UIElements.BaseVisualElementPanel panel, UnityEngine.UIElements.VisualElement target, System.Boolean isCapturingTarget) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.EventDispatchUtilities.DispatchToElementUnderPointerOrPanelRoot (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel, System.Int32 pointerId, UnityEngine.Vector2 position) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.EventDispatchUtilities.DispatchToCapturingElementOrElementUnderPointer (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel, System.Int32 pointerId, UnityEngine.Vector2 position) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.PointerMoveEvent.Dispatch (UnityEngine.UIElements.BaseVisualElementPanel panel) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.EventDispatcher.ProcessEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.EventDispatcher.Dispatch (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel, UnityEngine.UIElements.DispatchMode dispatchMode) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.BaseVisualElementPanel.SendEvent (UnityEngine.UIElements.EventBase e, UnityEngine.UIElements.DispatchMode dispatchMode) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.UIElementsUtility.DoDispatch (UnityEngine.UIElements.BaseVisualElementPanel panel) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.UIElementsUtility.UnityEngine.UIElements.IUIElementsUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr, System.Boolean& eventHandled) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.UIEventRegistration.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.UIElements.UIEventRegistration+<>c.<.cctor>b__1_2 (System.Int32 i, System.IntPtr ptr) (at <dfe5ebb180ed45a8a45a41aa8e736b59>:0)
UnityEngine.GUIUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr, System.Boolean& result) (at <4a6947576ef4457c8ad4707a19b6b683>:0)
I am on the latest Unity editor from yesterday and it says PlayMaker is up to date.