Mega menu active class

Hi gjr,
Seem you have duplicate menu item links in settings of Mega menu items. Please re-check.
Other way, let’s provide me the admin credentials of your site. I will check further and help you get out.
Regards,
Mall.

Hi gjr,

All the sub categories op producten do not work.

That because you have change the URL key of related categories after you added the menu item with that categories.
To solve the issues, you have to re-save all the related menu items. I have updated as examples with 2 menu items in your site: 
http://gjrshop.hypernode.io/communicatie.html
and
http://gjrshop.hypernode.io/educatie.html
and everything working fine.
Please have a look and contact me if you need further assistance!
Regards,
Mall.