Same error on WordPress 5.8.
"PHP message: WordPress database error You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '' at line 1 for query INSERT INTO 12c4h_mlw_question_terms (question_id, quiz_id, term_id, taxonomy) VALUES made by do_action('wp_ajax_enable_multiple_categories'), WP_Hook->do_action, WP_Hook->apply_filters, QSM_Migrate->enable_multiple_categories" while reading response header from upstream
