I found a lot of errors like these in the log file:
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 UPDATE wp_posts SET post_parent=35796 WHERE post_parent=0 AND ID IN () made by edit_post, wp_update_post, wp_insert_post, do_action('save_post_activity'), WP_Hook->do_action, WP_Hook->apply_filters, RW_Meta_Box->save_post, array_map, RW_Meta_Box->save_field, RWMB_Field::process_value, RWMB_Field::call, RWMB_Media_Field::value
I think it happens when editing and publishing custom posts, but everything seems to work fine. What does this error mean? It does not mention any post type or field ID.