I am experiencing exactly the same problem reported here. My validate value filters never get called. They are in my theme functions.php file and I have used the code provided above.
I am seeing acf/save_post work correctly btw. But acf/validate_value never does anything. Any help please? How do I debug this.
I am running a brand new WP site (as of a week ago) on PHP 5.4
To isolate this issue I dropped my child theme and I am using plain twentyseventeen. The only change is the top of functions.php as shown here
<?php
add_filter('acf/validate_value', 'my_acf_validate_value', 10, 4);
function my_acf_validate_value( $valid, $value, $field, $input ){
return "is that working?";
}
/**
* Twenty Seventeen functions and definitions
*
* @link https://developer.wordpress.org/themes/basics/theme-functions/
*
* @package WordPress
* @subpackage Twenty_Seventeen
* @since 1.0
*/
