I have a problem with the select_advanced with custom options load in ajax.
My ajax call is working well but when I choose a value and I click on "update", the page is saved properly except the value defined in the select.
I made a test on a fresh install of wordpress.
Wordpress : 5.6.2
Theme : Twenty Twenty-One 1.1
Meta Box : 5.3.8
Meta Box AIO : 1.13.4
I use Classic Editor extension but with or without the plugin the problem still the same.
You will find my code here
Put this file on your theme and u can make a simple include in the functions.php
I tried with a custom sanitize_callback seen on this topic but problem still the same
You will find a record here
Thanks for your support.