Call to undefined function __ecran_test_if_serialized()

Depuis la dernière mise à jour, j'ai des requêtes ajax qui plantent :

Fatal error: Uncaught Error: Call to undefined function __ecran_test_if_serialized() in /var/www/html/config/ecran_securite.php:663 Stack trace: #0 /var/www/html/ecrire/inc_version.php(87): include() #1 /var/www/html/spip.php(17): include_once('/var/www/html/e...') #2 {main} thrown in /var/www/html/config/ecran_securite.php on line 663

La requête en question, en GET :

https://machin.test/truc?var_ajax=form&formulaire_action=arbre_arbo&formulaire_action_args=***&formulaire_action_sign=***&...