When the Question statistics plugin is enabled, the following error may occur:

PHP Notice:  Error: mdb->get_record() found more than one record!<ul style="text-align: left" data-rel="backtrace"><li>line 1691 of /lib/dml/moodle_database.php: call to debugging()</li><li>line 1651 of /lib/dml/moodle_database.php: call to moodle_database->get_record_sql()</li><li>line 138 of /mod/quiz/report/statistics/classes/calculator.php: call to moodle_database->get_record_select()</li><li>line 657 of /mod/quiz/report/statistics/report.php: call to quiz_statistics
calculator->get_cached()</li><li>line 941 of /mod/quiz/report/statistics/report.php: call to quiz_statistics_report->get_all_stats_and_analysis()</li><li>line 2503 of /mod/quiz/lib.php: call to quiz_statistics_report->calculate_questions_stats_for_question_bank()</li><li>line 8075 of /lib/moodlelib.php: call to mod_quiz_calculate_question_stats()</li><li>line 88 of /question/bank/statistics/classes/helper.php: call to component_callback()</li><li>line 135 of /question/bank/statistics/classes/helper.php: call to qbank_statistics
helper::load_statistics_for in /var/www/html/lib/weblib.php on line 3295, referer: https://corsi.fadpsy.it/mod/quiz/view.php?id=551