please clear your cache and browsing history. then relogin, open notebook from the classroom page and wait for page to load. Also remember not to change the current browsing page to another until the files completely loads.
one also needs to check if their browser and system software is up-to-date if encountering any such loading issues.
It seems to have loaded fine today! Not sure what changed but If it comes up again I will try some of the steps listed above and comment here if further issues. Thanks all!