CoursePress Enroll Popup Problems

I am having multiple problems when trying to enrol in the default test course on one of my clients sites. When I'm logged in and I try to enrol, the popup background shows up, but not the actual popup. When I'm not logged in the popup does show up, but it stays on the loading screen. I tested this in both Chrome and Firefox. Here's the link to the course. This is a multisite setup and is not the main site. The theme used is Divi and the site-wide plugins activated are Broken Link Checker, CoursePress Pro, PopUp Pro, and WP Statistics. There are many network activated plugins, so I'll only list them if need. I already tried deactivating all site-wide plugins and switching themes. Thanks.