Steps to reproduce

• set backup_import_questionbank to no
• try to duplicate a quiz: it doesn't work
• set backup_import_questionbank back to yes (= default)
• duplicate quiz will work again.

Expected behaviour

Duplicating a quiz should work with backup_import_questionbank = 0. The reason for disabling import of question bank in my case is that when someone does an import of whatever from another course without disabling import of the question bank, the whole question bank of the source course gets imported. Therefore we promote moving quizzes with exporting and importing question categories rather then the import button.

In the logs I've found a few related php-notices apart from the whole flow of the action:

_[Wed Sep 30 10:45:47.340987 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] setting controller status to 100, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.349502 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] loading controller plan, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.361177 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] setting controller status to 300, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.366657 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] applying plan defaults, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.375484 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] setting controller status to 400, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.383870 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] setting file inclusion to , referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.392632 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] checking plan security, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.402191 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] setting controller status to 700, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.409680 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] saving controller to db, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.418210 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] calculating controller checksum fadc504fcad2fe7923d07eeac58be8bb, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.436442 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] loading controller from db, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.444001 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] setting controller status to 800, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.452318 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] saving controller to db, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.461035 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] calculating controller checksum 271bcb6685b59b8397b169ba6d862d00, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.496118 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] loading controller from db, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.511122 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] activity skipped by _included setting test, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.545082 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] setting controller status to 1000, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.546702 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] saving controller to db, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.556716 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] instantiating restore controller 53a987e9d131695e755060b6f908d1d4, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.564691 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] setting controller status to 100, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.573614 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] loading backup info, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.583958 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] PHP Notice: Undefined index: contents in /var/www/elo/moodle/backup/util/helper/backup_general_helper.class.php on line 196, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.584017 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] loading controller plan, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.591197 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] PHP Notice: Undefined index: in /var/www/elo/moodle/backup/moodle2/restore_plan_builder.class.php on line 136, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.591231 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] PHP Notice: Trying to get property 'modulename' of non-object in /var/www/elo/moodle/backup/util/factories/restore_factory.class.php on line 37, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.591269 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] setting controller status to 300, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.599214 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] applying restore defaults, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.608112 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] Unknown setting: questionbank, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.616498 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] Unknown setting: overwrite_conf, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.625291 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] Unknown setting: course_fullname, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.633715 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] Unknown setting: course_shortname, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.642449 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] Unknown setting: course_startdate, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.651426 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] Unknown setting: questionbank, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.659667 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] setting controller status to 400, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.668166 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] checking plan security, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.676811 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] setting controller status to 600, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.685264 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] saving controller to db, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.693948 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] calculating controller checksum 66db62de8479bc37c2b0e6122b340065, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.712090 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] loading controller from db, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.731795 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] setting controller status to 700, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.732863 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] saving controller to db, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.741691 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] calculating controller checksum 4bb78f2b3bd112b199870121bcd56c01, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.759441 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] loading controller from db, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.767117 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] setting controller status to 800, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.775501 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] saving controller to db, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.784280 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] calculating controller checksum f6ee899b564a6bf9fedb21f72e1c86ae, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.802221 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] loading controller from db, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.889794 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] processing file aliases queue, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
_[Wed Sep 30 10:45:47.926240 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] setting controller status to 1000, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1_
[Wed Sep 30 10:45:47.927578 2020] [php7:notice] [pid 4468] [client 84.198.108.220:46272] saving controller to db, referer: https://elo.ritacollege.be/moodle/course/view.php?id=1001&notifyeditingon=1

I have found that same error message in MDL-66221 which seems also being caused by changing a backup setting.