php - WordPress quick edit author change gives a "0" notice and fails

one text

I'm going crazy to understand the reason of this strange behavior.

I'm on WP (6.1), in maintenance mode (all plugins disabled). The reference URL is wp-admin/edit.php, with the latest 20 posts listed in the page. I want to modify, through the quick edit, the post author. When I change the author and click modify I receive this answer:

The network panel in the console admin reports a POST call like this:

mysite.com/wp-admin/admin-ajax.php?_fs_blog_admin=true

with this payload:

Tipo MIME: application/x-www-form-urlencoded; charset=UTF-8
post_title: Clima: nuovo blitz attivisti su Gra di Roma. La rabbia degli automobilisti
post_name: clima-nuovo-blitz-attivisti-su-gra-di-roma-la-rabbia-degli-automobilisti
jj: 02
mm: 11
aa: 2022
hh: 15
mn: 08
ss: 29
post_author: 35
post_password
post_category[]: 0
post_category[]: 25326
tax_input[post_tag]
_status: publish
_inline_edit: c291a5712d
post_view: list
screen: edit-post
action: inline-save
post_type: post
post_ID: 331431
edit_date: true
post_status: all

and this querystring param:

_fs_blog_admin: true

The call returns a 200 response code and a 0 written in the preview.

I've seen my server log and I've found just a row:

[03-Nov-2022 10:43:13 UTC] PHP Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'wp_ajax_inline_save' not found or invalid function name in /home/jxradioc/public_html/wp-includes/class-wp-hook.php on line 308

This is a simple warning, not a block.

Now I'm really confused about this because I cannot understand what could be the starting point of investigation.

If I change the author inside the post edit page, everything is ok.

Last consideration: this is a random error, sometimes (very rarely) works also with the quick edit way but is not systematic.

Thanks in advance for every suggestion.

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