Assertion failed: [File:D:\Build\++UE4\Sync\Engine\Source\Editor\UnreleasEd\Private\EditorServer.cpp] [Line: 1971] /Temp/Untitled 0.Untitled still around while trying to load new map (Object is not currently rooted)

Development World Creation
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1

Every time I open a level that exist in my project,
Create a new level and open it,
or create and open level from the c++ side,

I get this message:

[2019.07.26-23.55.53:583][344]LogReferenceChain:   
[2019.07.26-23.55.53:747][344]LogOutputDevice: Warning: 

Script Stack (0 frames):

[2019.07.26-23.55.53:747][344]LogWindows: Windows GetLastError: The operation completed successfully. (0)
[2019.07.26-23.55.54:629][344]LogWindows: Error: === Critical error: ===
[2019.07.26-23.55.54:629][344]LogWindows: Error: 
[2019.07.26-23.55.54:629][344]LogWindows: Error: Fatal error: [File:D:\Build\++UE4\Sync\Engine\Source\Editor\UnrealEd\Private\EditorServer.cpp] [Line: 1971] 
[2019.07.26-23.55.54:629][344]LogWindows: Error: /Temp/Untitled_0.Untitled still around while trying to load new map
[2019.07.26-23.55.54:629][344]LogWindows: Error:    (Object is not currently rooted)
[2019.07.26-23.55.54:629][344]LogWindows: Error: 
[2019.07.26-23.55.54:629][344]LogWindows: Error: 
[2019.07.26-23.55.54:629][344]LogWindows: Error:

What does “Object is not currently rooted”?

2

Have the same problem 50% of time when I open new map I get the same messagelink text