We are on Moodle 3.5.5 (Build: 20190311) and currently using the Adaptable theme.
I have an instructor, who was duplicating multiple quizzes, each with random questions, in one of her courses yesterday, who can not duplicate anything in any of her courses today. She is the only user with this issue at this time.
There are references to a similar issue in the following discussions
https://moodle.org/mod/forum/discuss.php?d=378965
https://moodle.org/mod/forum/discuss.php?d=376633
https://moodle.org/mod/forum/discuss.php?d=365101
but both bug trackers indicate that problem was fixed in Moodle versions
3.5.4, 3.6.2:
https://tracker.moodle.org/browse/MDL-63260
https://tracker.moodle.org/browse/MDL-60604