We currently have 2 running Moodles, one running in 1.9.10 and one in 1.9.12. We're in the process of migrating content from the older one into the newer one, by backing up and restoring all the courses.
Yesterday morning, the older one developed a fault with the My Courses block: beyond a certain point in the list, each category only lists one course from those it contains (not always the same one either, depending on your role!). We continued the migration process and, a few hours later, the newer Moodle developed the same fault.
We're assuming it's something to do with one of the courses when it was backed up / restored, so are in the process of deleting everything we did yesterday, but has anyone experienced this before, or does anyone have any ideas what we might check?