Crash on duplicating

Message from server:

AH01071: Got error ‘PHP message: PHP Fatal error: Uncaught Error: The script tried to modify a property on an incomplete object. Please ensure that the class definition “Wpil_Model_Link” of the object you are trying to operate on was loaded _before_ unserialize() gets called or provide an autoloader to load the class definition in /var/www/vhosts/contality.de/httpdocs/wp-includes/formatting.php:5022\nStack trace:\n#0 /var/www/vhosts/contality.de/httpdocs/wp-includes/formatting.php(5017): map_deep()\n#1 /var/www/vhosts/contality.de/httpdocs/wp-content/plugins/duplicate-post/admin-functions.php(400): map_deep()\n#2 /var/www/vhosts/contality.de/httpdocs/wp-content/plugins/duplicate-post/admin-functions.php(424): duplicate_post_addslashes_deep()\n#3 /var/www/vhosts/contality.de/httpdocs/wp-content/plugins/duplicate-post/admin-functions.php(386): duplicate_post_wp_slash()\n#4 /var/www/vhosts/contality.de/httpdocs/wp-includes/class-wp-hook.php(310): duplicate_post_copy_post_meta_info()\n#5 /var/www/vhosts/contality.de/httpdocs/wp-includ…’, referer: https://www.contality.de/wp-admin/edit.php?s=ads&post_status=all&post_type=post&action=-1&m=0&cat=0&seo-filter&paged=1&action2=-1