Colorbox not working at all pages?

I installed the Colorbox plugin and it works fine on all WordPress content, however not all static links in the theme!

For instance it works fine here (click the red link):
https://awmedar58.fiftyeight.axc.nl/temp2/blog/

But not here (click the red link):
https://awmedar58.fiftyeight.axc.nl/temp2/projecten/

Both links are the same:
Click me!

Any explanation?

thanks

https://www.ads-software.com/plugins/jquery-colorbox/