We (seemingly) randomly had the following error :

    line 236 of /lib/modinfolib.php: moodle_exception thrown
    line 1890 of /lib/modinfolib.php: call to course_modinfo->get_cm()
    line 1078 of /lib/completionlib.php: call to cm_info::create()
    line 70 of /completion/classes/cm_completion_details.php: call to completion_info->get_data()
    line 275 of /completion/classes/cm_completion_details.php: call to core_completion\cm_completion_details->__construct()
    line 947 of /course/renderer.php: call to core_completion\cm_completion_details::get_instance()
    line 836 of /course/renderer.php: call to core_course_renderer->course_section_cm()
    line 1051 of /course/renderer.php: call to core_course_renderer->course_section_cm_list_item()
    line 859 of /course/format/renderer.php: call to core_course_renderer->course_section_cm_list()
    line 57 of /course/format/topics/format.php: call to format_section_renderer_base->print_multiple_section_page()
    line 278 of /course/view.php: call to require()

By checking the offending data in one of the cases, here are some more details :

When code reaches this point $cmid equals 1128369 (mod_zoom), but $this->cms only contains [1128368](mod_forum).

When checking the course_modules DB table for this course, I find the correct two course modules :

> SELECT * FROM mdl_course_modules WHERE course = 21942;

Module 7 is mod_forum, whereas module 48 is mod_zoom.

I noticed that this involves some weird "ghost" module instance, having mdl_course_modules.instance = 0 (as per the example query result above).

So far, I've encountered cases involving mod_forum, mod_zoom, mod_scorm, and mod_assign – so it does not look like a bug related to any of these in particular.

Checking further, $this->cms never contains any of these "ghost" modules, and they are never displayed on the course page. Trying to force their display (by browsing to /mod/<modulename>/view.php?id=<cm.instance>) obviously does not work either – it yields the same exception in course_modinfo::get_cm().

I then checked what had changed on our Moodle installation recently, noting that I had just upgraded from Moodle 3.11.2 to 3.11.3 earlier on the same day.

Looking at the changes made in one of the fixed issues (from the [Moodle 3.11.3 release notes|https://docs.moodle.org/dev/Moodle_3.11_release_notes),] I noticed one that was related to improve performance of activity information (and completion) : MDL-71899.

I then just reverted this line, and it seemed to fix the problem :

https://github.com/HuongNV13/moodle/compare/7fdf72a268...MDL-71899-311-2#diff-37fe4a6388ccfbca35d5fb6457580fcba1dcd3e6737aa7f522336890b0536506R68