We are currently running Moodle version 3.3+ (Build: 20170519) and were not experiencing any issues until one of our sysadmins chose to "Purge all caches":
Site administration > Development > Purge all caches
After the caches were purged, we have been unable to successfully manage courses by clicking the "manage courses" button. The following appears when in debug mode:
PHP Warning: Invalid argument supplied for foreach() in /var/www/moodle-courses/web33/cache/classes/loaders.php on line 519, referer: https://courses.caltech.edu/course/management.php?categoryid=979
When debug mode is switched off, nothing appears to happen. However, when debug mode is switched on we are taken to a page which says:
"This page should automatically redirect. If nothing is happening please use the continue link below.