Moodle version 3.11
My Moodle site is experiencing a serious glitch.
I have been duplicated activities (quiz) many times (before version 3.11) and everything is fine.
However, when I tried to duplicate activities today, the duplicated activities didn't show on the main course page. I felt strange and refreshed the page, the duplicated activities appeared. Then I moved the appeared duplicated activities to another topic. But when I refreshed again, the duplicated activities that had just appeared disappeared again.
What's worse, all the quiz, workshop activities and Grades are now not working properly. They all show the same error: Invalid course module ID.
It seems that the duplicated activities exist, but for some reason they can't display properly and break the system. When I created a new course and import data from the old one, the disappeared duplicated activites appear on the import checklist. (BTW, the import is unsuccessful)
What should I do to get the site back to normal? Is it possible to delete the disappeared duplicated activites?