Update Users with additional Field

Hi,

we created a function to add a new field:

function custom_user_merge_tags($merge_vars, $user) {
   
	// Get the WP_User ID
    $user_id = $user->ID;
	// Get the WP_User roles and capabilities
    $user_roles = $user->roles;
	// Letzte User Rolle im Array ist die Händlergruppe
	$client_user_role = end($user_roles);
	/// add whatever you want to the merge tags
    $merge_vars['USERROLLE'] = $client_user_role;
   
    return $merge_vars;
}

add_filter('mailchimp_sync_user_mergetags', 'custom_user_merge_tags', 100, 2);

As soon as a new user registers it works fine. But i can’t update existing users.
If i click resync nothing happens. Users are not updated.

Any ideas?

thx
Chris