When I look at the design versus the live view of the calendar I only see one selectable category in the live view, whereas the design has four. Furthermore, the non-selectable categories are not even displayed on the calendar!
This is what it should look like (marking the parts missing in the live view):
And this is what the live view looks like (in the language of the site):
That’s a big and very important difference. Where did my categories go??
I use version 3.5.4 of the plugin on a Minimal Muse 1.3.8. theme with custom CSS. And I’m pretty sure it’s not the custom CSS doing this.