IE 11 - Course not playing in production site but does outside

Has anyone run into this? I create a monthly course for a client using Storyline 360. I use the same course template(and have been for almost 2 years) and just change images, text and audio files. For some reason, this month the course will not load in IE 11 within the clients production site. It does outside however. The only thing that has changed was a few days ago I did the latest update to Storyline. I have since reverted back to the older version, but it still will not play. 

I am and have been exporting as HTML5 with Flash fallback, but to test I tried just HTML5 and the course still will not load. We just get a blank page. It works fine in other browsers, unfortunately we need it to work in all. I have also republished last months course, which worked fine last month but not this month. Interestingly, the published file from last month does work as a current upload, so its anything published recently. Again, I reverted back to the previous version and it will wont work. Its hard to know if it is something in the software or not!

Also, as a side note - I have and always have exported the file for web, not LMS. They say nothing has changed on their end - so I am at a loss at this point. Anyone have any ideas what we could try next?