Error when duplicating quiz

Dear devs,

When I try to copy an existing quiz, I get an error message. Could you take a look at this? I have included the error message.

Foutdetails
===========
Een fout van het type E_ERROR werd veroorzaakt op regelnummer 911 van het bestand /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-content/plugins/quiz-master-next/php/classes/class-qmn-quiz-manager.php. Foutmelding: Uncaught TypeError: count(): Argument #1 ($value) must be of type Countable|array, string given in /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-content/plugins/quiz-master-next/php/classes/class-qmn-quiz-manager.php:911
Stack trace:
#0 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-content/plugins/quiz-master-next/php/classes/class-qmn-quiz-manager.php(506): QMNQuizManager->display_quiz(Object(stdClass), Array, 0, Array)
#1 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-includes/shortcodes.php(355): QMNQuizManager->display_shortcode(Array, '', 'mlw_quizmaster')
#2 [internal function]: do_shortcode_tag(Array)
#3 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-includes/shortcodes.php(227): preg_replace_callback('/\\[(\\[?)(mlw_qu...', 'do_shortcode_ta...', '[mlw_quizmaster...')
#4 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-includes/class-wp-hook.php(308): do_shortcode('[mlw_quizmaster...')
#5 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-includes/plugin.php(205): WP_Hook->apply_filters('[mlw_quizmaster...', Array)
#6 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-content/plugins/wordpress-seo/src/builders/indexable-link-builder.php(115): apply_filters('the_content', '[mlw_quizmaster...')
#7 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-content/plugins/wordpress-seo/src/integrations/watchers/indexable-post-watcher.php(207): Yoast\WP\SEO\Builders\Indexable_Link_Builder->build(Object(Yoast\WP\SEO\Models\Indexable), '[mlw_quizmaster...')
#8 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-includes/class-wp-hook.php(310): Yoast\WP\SEO\Integrations\Watchers\Indexable_Post_Watcher->build_indexable(65983)
#9 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-includes/class-wp-hook.php(332): WP_Hook->apply_filters(NULL, Array)
#10 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-includes/plugin.php(517): WP_Hook->do_action(Array)
#11 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-includes/post.php(4726): do_action('wp_insert_post', 65983, Object(WP_Post), false)
#12 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-content/plugins/quiz-master-next/php/classes/class-qmn-quiz-creator.php(522): wp_insert_post(Array)
#13 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-content/plugins/quiz-master-next/php/admin/quizzes-page.php(248): QMNQuizCreator->duplicate_quiz(529, 'Koude Oorlog: v...', 0)
#14 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-includes/class-wp-hook.php(308): QSMQuizList->qsm_process_post_row_actions('')
#15 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-includes/class-wp-hook.php(332): WP_Hook->apply_filters('', Array)
#16 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-includes/plugin.php(517): WP_Hook->do_action(Array)
#17 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-admin/admin.php(385): do_action('load-edit.php')
#18 /var/www/vhosts/geschiedenisvandaag.nu/httpdocs/wp-admin/edit.php(10): require_once('/var/www/vhosts...')
#19 {main}
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