Replication steps

1. Create course.
2. Add a module (lesson).
3. Delete the lesson.
4. Disable the module ['Site administration > Plugins > Activity modules > Manage activities'].
5. Run the cron.
6. Refresh the manage activities page and notice that the lesson count has decreased.
7. Check the recycle bin in the course for the deleted activity.
8. Try in vain to enable the module again in the hopes that the activity will reappear somewhere.

• Module seems have disappeared.