This is a question I've been meaning to ask for quite some time and always postponed.
In a Jupyter notebook (v6.0.1) I constantly find myself having to switch backends between %matplotlib inline and %matplotlib widget (i.e. ipympl). Whenever I go from inline to widget, I have to run the cell several times and, somehow, "with the right timing", so that the backend actually kicks in. Any ideas as to why?