Risposta json non valida

Da ieri non riesco più a modificare pagine e articoli di nessuno dei miei siti in locale. Ottengo sempre il messaggio di errore “Pubblicazione non riuscita. Risposta json non valida” e la console di Chrome mi riporta la seguente sfilza di errori di ajax:

Uncaught TypeError: $ is not a function
at admin.js?ver=5.4.1:1
deprecated.min.js?ver=cd9e35508705772fbc5e2d9736bde31b:2 wp.editor.withColors is deprecated. Please use wp.blockEditor.withColors instead.
c @ deprecated.min.js?ver=cd9e35508705772fbc5e2d9736bde31b:2
/wp-json/wp/v2/:1 Failed to load resource: the server responded with a status of 404 (Not Found)
wp-api.min.js?ver=5.4.1:2 i
post.php?post=1059&action=edit:1 [DOM] Found 2 elements with non-unique id #_wpnonce: (More info: https://goo.gl/9p2vKq) <input type=​”hidden” id=​”_wpnonce” name=​”_wpnonce” value=​”bc279b8c35″>​ <input type=​”hidden” id=​”_wpnonce” name=​”_wpnonce” value=​”054a5caf8a”>​
/wp-json/wp/v2/users/me?_locale=user:1 Failed to load resource: the server responded with a status of 404 (Not Found)
/wp-json/wp/v2/users/?who=authors&per_page=100&_locale=user:1 Failed to load resource: the server responded with a status of 404 (Not Found)
data.min.js?ver=e80048e7b309581a40e44b8bd8aaba41:2 Uncaught (in promise) Response
data.min.js?ver=e80048e7b309581a40e44b8bd8aaba41:2 Uncaught (in promise) Object
/wp-json/wp/v2/taxonomies/post_tag?context=edit&_locale=user:1 Failed to load resource: the server responded with a status of 404 (Not Found)
data.min.js?ver=e80048e7b309581a40e44b8bd8aaba41:2 Uncaught (in promise) Object
/wp-json/wp/v2/posts/1059?_locale=user:1 Failed to load resource: the server responded with a status of 404 (Not Found)
api-fetch.min.js?ver=b437dd9d1118e698b1b85961e759bf03:2 POST http://www.olivishop.demo/wp-json/wp/v2/posts/1059/autosaves?_locale=user 404 (Not Found)

Ho provato a cambiare i permalink, a eliminare e ricreare il file htaccess, ma niente. Persevera nell’errore e non riesco a risolvere. Non so più dove sbattere la testa.