Single Portfolio-item gives Error 404

Hello WP-ers,

I am setting up an website by using Avada. I would like to display portfolio-items on the Participating Suppliers page. That page shows the categories and items, but when I click on the single item it gives an Error 404. All permalinks et cetera are correct. I also disabled plugins, but the problem is still present.

I ask you for help.

Thanks ??

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