Another user reported the same issue.

She was using Google Chrome. Tested this on IE, Firefox, Safari, and Android Browser as well (for the last two browsers, the page became unresponsive).

For other pages, there were no issues in adding widgets on the page. Only for one page.

Page URL: https://www.openlearning.com/courses/basic-quantities-for-quantity-surveyors/measurement_of_site_clearance_works

That looks familiar. haven't seen it since Tuesday though