Strange log error when using the engine

Hello everyone, I’m having a strange log error from time to time when using engine 4.13, it happens when a blueprint is open, it freeze the engine for few seconds, then in the output log appear this error:

LogUObjectArray:Warning: Other object in slot
LogStats: FPlatformStackWalk::StackWalkAndDump - 18.051 s
LogOutputDevice:Error: === Handled ensure: ===
LogOutputDevice:Error: Ensure condition failed: false [File:D:\Build\++UE4+Release-4.13+Compile\Sync\Engine\Source\Editor\UnrealEd\Private\Kismet2\KismetDebugUtilities.cpp] [Line: 1018]
LogOutputDevice:Error: Error: Invalid (but non-null) property associated with pin; cannot get variable value
LogOutputDevice:Error: Stack: 
LogOutputDevice:Error: UE4Editor-Core.dll!FWindowsPlatformStackWalk::StackWalkAndDump() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\private\windows\windowsplatformstackwalk.cpp:183]
LogOutputDevice:Error: UE4Editor-Core.dll!FDebug::EnsureFailed() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\private\misc\outputdevice.cpp:297]
LogOutputDevice:Error: UE4Editor-Core.dll!FDebug::OptionallyLogFormattedEnsureMessageReturningFalse() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\private\misc\outputdevice.cpp:432]
LogOutputDevice:Error: UE4Editor-UnrealEd.dll!FKismetDebugUtilities::GetWatchText() [d:\build\++ue4+release-4.13+compile\sync\engine\source\editor\unrealed\private\kismet2\kismetdebugutilities.cpp:1018]
LogOutputDevice:Error: UE4Editor-BlueprintGraph.dll!UK2Node::GetPinHoverText() [d:\build\++ue4+release-4.13+compile\sync\engine\source\editor\blueprintgraph\private\k2node.cpp:1219]
LogOutputDevice:Error: UE4Editor-GraphEditor.dll!SGraphPin::GetTooltipText() [d:\build\++ue4+release-4.13+compile\sync\engine\source\editor\grapheditor\private\sgraphpin.cpp:976]
LogOutputDevice:Error: UE4Editor-GraphEditor.dll!TMemberFunctionCaller<SGraphPin,FText (__cdecl SGraphPin::*)(void)const __ptr64>::operator()<>() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\public\delegates\delegateinstanceinterface.h:161]
LogOutputDevice:Error: UE4Editor-GraphEditor.dll!TTupleImpl<TIntegerSequence<unsigned int> >::ApplyAfter<TMemberFunctionCaller<SGraphPin,FText (__cdecl SGraphPin::*)(void)const __ptr64> >() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\public\delegates\tuple.h:115]
LogOutputDevice:Error: UE4Editor-GraphEditor.dll!TBaseSPMethodDelegateInstance<1,SGraphPin,0,FText __cdecl(void)>::Execute() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:317]
LogOutputDevice:Error: UE4Editor-Slate.dll!TBaseDelegate<FText>::Execute() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\public\delegates\delegatesignatureimpl.inl:521]
LogOutputDevice:Error: UE4Editor-Slate.dll!TAttribute<FText>::Get() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\public\misc\attribute.h:135]
LogOutputDevice:Error: UE4Editor-Slate.dll!SToolTip::IsEmpty() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\slate\private\widgets\stooltip.cpp:84]
LogOutputDevice:Error: UE4Editor-Slate.dll!FSlateApplication::UpdateToolTip() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:3338]
LogOutputDevice:Error: UE4Editor-Slate.dll!FSlateApplication::ProcessMouseMoveEvent() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:5523]
LogOutputDevice:Error: UE4Editor-Slate.dll!FSlateApplication::OnMouseMove() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:5478]
LogOutputDevice:Error: UE4Editor-Core.dll!FWindowsApplication::ProcessDeferredMessage() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\private\windows\windowsapplication.cpp:1622]
LogOutputDevice:Error: UE4Editor-Core.dll!FWindowsApplication::DeferMessage() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\private\windows\windowsapplication.cpp:1930]
LogOutputDevice:Error: UE4Editor-Core.dll!FWindowsApplication::ProcessMessage() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\private\windows\windowsapplication.cpp:747]
LogOutputDevice:Error: UE4Editor-Core.dll!FWindowsApplication::AppWndProc() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\private\windows\windowsapplication.cpp:669]
LogOutputDevice:Error: USER32.dll
LogOutputDevice:Error: USER32.dll
LogOutputDevice:Error: UE4Editor-Core.dll!FWindowsPlatformMisc::PumpMessages() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\core\private\windows\windowsplatformmisc.cpp:905]
LogOutputDevice:Error: UE4Editor.exe!FEngineLoop::Tick() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\launch\private\launchengineloop.cpp:2788]
LogOutputDevice:Error: UE4Editor.exe!GuardedMain() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\launch\private\launch.cpp:156]
LogOutputDevice:Error: UE4Editor.exe!GuardedMainWrapper() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:126]
LogOutputDevice:Error: UE4Editor.exe!WinMain() [d:\build\++ue4+release-4.13+compile\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:202]
LogOutputDevice:Error: UE4Editor.exe!__scrt_common_main_seh() [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:264]
LogOutputDevice:Error: kernel32.dll
LogOutputDevice:Error: ntdll.dll
LogOutputDevice:Error: ntdll.dll
LogStats:                SubmitErrorReport -  0.000 s
LogStats:                    SendNewReport -  1.393 s
LogStats:             FDebug::EnsureFailed - 19.451 s
LogUObjectArray:Warning: Other object in slot
LogUObjectArray:Warning: Other object in slot
LogUObjectArray:Warning: Other object in slot
LogUObjectBase:Warning: Object is not registered
LogUObjectBase:Warning: Object is not registered
LogUObjectBase:Warning: Object is not registered
LogUObjectBase:Warning: Object is not registered
LogUObjectBase:Warning: Object is not registered
LogUObjectBase:Warning: Object is not registered
LogUObjectBase:Warning: Object is not registered
LogUObjectBase:Warning: Object is not registered

I don’t know what this means, it didn’t happen in previous engine versions, if someone with knowledge can explain this and know how to fix it, it will be very helpful.

Thank you.