rwmb_frontend_validate still passes when $validate is a string

Hi

I have used the metabox front end forms for a long time and since upgrading metabox front end forms addon/extension the validation does not work anymore? it always passes. I have loads of different posts, model setups.

e.g. shortcode
[mb_frontend_form id="dc-product" confirmation="Your post has been successful" ajax="true"]

add_filter( 'rwmb_frontend_validate', function( $validate, $config ) {
    // Check only if you're on the right form.
    if ( 'dc-product' !== $config['id'] ) {
        return $validate;
    }

    error_log(print_r($config, true));
    $validate = 'example error'; // Return false to show an error message.
    
    return $validate;
}, 10, 2 );

The form shows in the error logs so no issues but its stopped working for posts, models, if i force the value for $validate to be false or a string it still ignores it. No error message appears, just your 'Your post has been successful' message.

using MB Frontend Submission v4.5.5

thanks

Nick