An item with the same key has already been added - Argument Exception

Hey, I have been experiencing the weirdest situation. When trying to create an editor window I get this warning. It’s really weird since my class is empty.

The weirdest thing even, is that I recreated this problem in an empty project: I created a empty project I added a script with a class inheriting from Editor window and the warning just popped up. Has anyone every experience anything alike?

Where did you create that class? Inside the Unity editor or inside visual studio? Keep in mind that Visual Studio is just an editor and all project relevant details are handled by Unity. Have you tried saving the file, switching to the Unity editor, waiting for the actual recompile and then switch back? I usually create scripts inside the Unity editor and never had any issues like that.

I created normally in the Unity Editor and just made the changes to inherit from Editor Window.
As I said I even tried with an empty project with some random class name and I still got the warning.

I’m using Unity 2019.3.10f1, maybe it’s some issue with this version I don’t know. In any case, the warning was annoying me so I just used other tool and ditched the editor window idea altogether.