ACF load user_meta cross WordPress multisite

Users are global in a multisite. And default ACF groups are per site. So if you set a pinterest url for a user on one site it will apply it for all sites. No problem. But if you set an image it will try to find that image-id on each site.

The solution.

Step 1; Limit the user acf groups only to the main site:

function wpstarter_filter_fields_group($result, $rule, $screen) {
    if ( isset( $screen['user_id'] ) && ! is_main_site() )
        return false;

    return $result;
}
add_filter('acf/location/rule_match', 'wpstarter_filter_fields_group', 10, 3);

Step 2; Get image fields for users only from the main site:

function wpstarter_load_avatar_value_cros_site( $value, $post_id, $field ) {

    if( 0 !== strpos( $post_id, 'user_' ) || is_main_site() ) {
        return $value;
    }

    switch_to_blog( get_main_site_id() );

    $value_of_main_site = acf_get_value($post_id, $field);
    $value              = acf_format_value($value_of_main_site, $post_id, $field);

    restore_current_blog();
    return $value;
}
add_filter( 'acf/format_value/type=image', 'wpstarter_load_avatar_value_cros_site', 11, 3);