As admin, go to any course page on your test system. Enrol a test user account in the course (or use an existing one). Open a second browser, go to the same course page, and log in using the test account. Make a code change (just for testing) to lib/modinfolib.php: Search for the comment: // Retrieve all information about activities and sections. Immediately above this line, add the following line: sleep(10); debugging('Actually building course cache'); Using the admin browser, edit course settings. Without making a change, click Save and display Using the other (user) browser, load the course page again. (You need to do this step within ten seconds - ideally a couple of seconds after hitting save in the admin browser.) EXPECTED: The admin browser takes 10 seconds then displays debugging info about rebuilding the course cache. EXPECTED: The other browser finishes slightly faster - it should load immediately after the admin browser does.There should be no debugging info. In the admin browser, open a new tab on the Site administration page, and go to Plugins / Caching / Configuration . Find the coursemodinfo cache area, and click Purge next to it (if you can't see that link, try making your browser ginormously wide). Wait for this to finish. In the user browser, reload the course page. In the admin browser, go back to the course page tab and reload it. EXPECTED: The user browser takes 10 seconds then displays the page, including debugging info about rebuilding the course cache. EXPECTED: The admin browser finishes immediately after the user browser does, and there should be no debugging info.