Hosting Plan Cart template shows different in safari and chrome/firefox

I'm using the above named WPMU plugin for my hosting website.
Everything works fine in safari, but when I use Chrome or Firefox, the used WHMCS cart template "Slider" doesn't show but a different undefined is shown (I did also test with the comparison template).

Here's the URL where you can see the specific page:

https://wphosting.club/members/whmsportal/cart.php/?gid=2

Thanks in advance

Guy