Hey there,
Looks like there might be some issues with the Fancy box plugin being used. You might want to try and disable all plugins and activating one by one to find the culprit. Looks like a possible issue between the styling and the plugin itself causing an issue. Hope that’s a start to help track down the issue.
Thank you for your help Will! Unfortunately it didn’t work, I had already deactivated my Fancybox plugin and it is not part of the problem. The filter won’t work, even with all the plugins deactivated 🙁