It seems that when a section of the Visual Logger is detached from the window as a whole and then that window is closed when docked next to the Content Browser, then the engine crashes. However, when the Visual Logger is docked at the top tab bar where the open map is docked by default, then detaching a section of the window and closing said window doesn't crash the editor.
Tested in //UE4/Release-4.26 @ CL 15973114 and this occurred, so not marking as a Regression.
The editor crashes
The editor doesn't crash when closing the Visual Logger window when not all of it's components are docked within it
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-135473 in the post.