I also have the same issue but I a not using transparent images
from the javascript console:
Request URL: http://ticketserv.com/support/index.php/courses/test-course/test-lesson-a?_=1438061907285
Request Method: GET
Status Code: HTTP/1.1 404 Not Found
I have submitted some more info through the contact form.
I have checked the javascript console and the issue seems to be 404 not found on the lessons:
i.e. http://ticketserv.com/support/index.php/courses/test-course/test-lesson-a
is not found – I get “Oops! That page can’t be found.” from wordpress
