Upgraded to 3.11 and now noticing the dashboard is loading very slowly at times. I have the dashboard set to display 12 courses.

Using MySQL 8.0, checking "htop" I see that MySQL is the most active process when I run the tests.

Using the "inspector" in the browser, I narrowed the area that takes the longest to return.

https://[mymoodle]/lib/ajax/service.php?sesskey=Vsvzu2sm2d&info=core_course_get_enrolled_courses_by_timeline_classification

I tested it by purging cache in another browser before logging in. After the slow load, the next reload of the page is very quick. It seems that the cache works for some time. After accessing a few courses and then later on returning to the dashboard, I again see a slow loading time of 30 seconds. 

Prior to the upgrade, this page took less than 1 second to load.

I also removed all the analytics code we have in Additional HTML to ensure that wasn't the source of any issue, and it made no difference.

STEPS TO RECREATE:

1. Activity completion must be enabled in multiple courses.
2. The courses should have a number of activities that are tracking completion.
3. The role should be a Student (or Teacher who also has the role of student in the courses).
4. Clear the site cache.
5. Log in as the user with a few (more than 3) courses that have completion tracking enabled.
6. Wait up to 30 seconds for the dashboard to appear.

It is really prevalent in our users who are doing content creation in multiple classes. They have completion tracking enabled, they are connected with multiple courses, and sometimes they assume the role of student in order to test things out.

However, if a student happens to be enrolled in a few of these courses, their dashboard takes over 10 seconds to display each time they log in and each time they complete activities.