Hi,
It is due to an internal limitation (performance reasons), where the keyword logic applies to the whole of the field, and not the individual fields. It is possible to bypass that limit with a small custom code snippet. That should resolve the issue.
To add the bypass, please add this custom code to the functions.php in your theme/child theme directory. Before editing, please make sure to have a full site back-up just in case!
add_action('asp_query_args', 'asp_query_args_meta_changes');
function asp_query_args_meta_changes($args) {
$args['user_search_meta_fields_separate_subquery'] = 1;
return $args;
}If you need help with it, you can add temporary FTP details, and I will do it for you.