Box greys out instead of loading

Hi, my links have recently stopped loading boxes and now grey out the screen when clicked. I’ve tested this on multiple pcs and mobile phone.

Plugin is up to date.
My server is using PHP 5.6, but I have 7.0 through to 7.3 available.

Boxzilla settings are:
Enable test mode: Yes
Load this box if request matches ANY of the following conditions: EVERYWHERE
Box position: center
Animation: slide in
Autobox show: never

Thank you. Would appreciate any help.

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