Many Open edX platforms broke a few days ago when the CDN that hosts Mathjax changed from cdn.mathjax.org to cdnjs.cloudflare.com.
Ned Batchelder, an engineering lead at edX, explained on Google Groups that platforms on Ficus 2 should be updated to Ficus 3 immediately.
However, this issue affects all platforms that are older than Ficus 2 (including Eucalyptus). As such, you may have seen the following error:
In order to manually apply the Mathjax patch to these instances, follow the steps detailed in this commit from edX on April 12 and add the following to lms/envs/common.py.
Then, remember to restart edxapp and update the assets to kick the changes into effect:
Mathjax’s CDN should now be upgraded and the platform be good to go!