Enhanced Editor hanging when using Safari, Chrome and Firefox, works for Explore

Hi
I am having trouble with a site I’m designing. When I go in the backend of a page in wordpress Yoast loads however the advanced editor doesn’t. The only way to get it to load is to click the default editor button and click back to the advanced editor. The odd thing is I tested this on 5 devices (4 Macs and 1 PC) and the PC doesn’t have this issue only the Macs. So I tested it on Firefox, Google Chrome and Safari and sure enough the hanging happened on all of them. Have you ever heard of an issue like this? It’s really frustrating because I use you theme all the time and have never experienced this. The only difference is that it is hosted with someone else so I don’t know if they need to do something their end to make it work. If you can possibly steal me in the right direction that would be greatly appreciated.
cheers Kinnear