menu displayed differently in project pages

Hi,

I’m having an issue with the vertical menu on the link mentioned: it displays expanded and without arrows where it should be displayed collapsed (like on this page; https://imaginatie.dewebconnectie.nl/scholing/). So, on a normal page it displays how it should, but on a project page (course) or post it dispays the wrong way.

How can i fix this?

Regards, Ester

The page I need help with: [log in to see the link]