When we attempt to backup a course into an IMS Common Cartridge, it seems that question banks and quiz activities are not being included.  

When creating these from a course, we:

1. Select Course Settings -> Backup
2. Uncheck "Include enrolled users"
3. Check "IMS Common Cartridge 1.1"
4. Jump to the final step
5. Download the backup from Moodle

If I explore the .imscc file by changing the extension to .zip and extracting everything, you can see that the imsmanifest.xml file does not include any question bank or quiz information.

If I do the same for an older cartridge that we created in Moodle 3.x, the imsmanifest.xml is much larger and points to subdirectories within the archive that contain assessment.xml files.