PHP settings:

post_max_size = 20M
upload_max_filesize = 20M

Moodle site-wide settings:

maxbytes = 20 Mb
assignment_maxbytes = 20 Mb

Course specific setting:

maxbytes = 20 Mb

However, when we create an "Advanced uploading of files" assignment as part of this course and edit its settings, the maximum size we can select from the drop-down menu is 8 Mb as this is what the system believes the course upload limit to be, which it isn't. It's 20 Mb, and we have confirmed this by checking the course settings.

In short, the "Advanced uploading of files" assignment has an incorrect idea of what the course upload limit is.