Window's Snap Assist does not find my electron application
Snap Assist will only display windows that are resizable. If your window is initially not resizable, then you won't be able to snap it to one side.
Update: I see now that this happens if you set resizable to false, and then make it resizable later via setResizable(true).
This issue is being tracked here.
I know that this thread is fairly old. Although, had the same issue just recently. For me removing transparent : true when creating the BrowserWindow object fixed it.