Relationship working on Author page but not Post

Edit: you'll see post-type declared as licensee above instead of provider. Ignore that - I was trying it because I use a slug rewrite. But the result is the same with both.

Views already offers the {{ author.ID }} variable, why can't I use that? I tried it and it makes the whole page break.

That said, to verify the code is working in the first place I replaced UserID with the value 7 (user ID of the author of a post I'm testing the View on) and it's still not showing anything...

Are you sure the code you provided is sound?

Sure thing, in fact I can paste the generated PHP code for the relationship:

<?php
add_action( 'mb_relationships_init', 'your_prefix_function_name' );

function your_prefix_function_name() {
    MB_Relationships_API::register( [
        'id'   => 'user-provider',
        'from' => [
            'object_type'   => 'user',
            'post_type'     => 'licensee',
            'taxonomy'      => 'category',
            'empty_message' => 'Not affiliated with a Provider',
            'admin_column'  => [
                'position' => 'after title',
                'title'    => 'Affiliation',
                'link'     => 'view',
            ],
            'meta_box'      => [
                'title'   => 'Provider you\'re affiliated with',
                'context' => 'normal',
                'style'   => 'seamless',
            ],
        ],
        'to'   => [
            'object_type'  => 'post',
            'post_type'    => 'licensee',
            'admin_column' => [
                'position' => 'after title',
                'title'    => 'Affiliated',
                'link'     => 'view',
            ],
            'meta_box'     => [
                'title'    => 'User accounts associated with this licensee',
                'context'  => 'normal',
                'priority' => 'high',
            ],
            'field'        => [
                'name' => 'Affiliated Licensee',
            ],
        ],
    ] );
}

But if you want a screenshot from the UI here is one https://i.imgur.com/vYJ3QdK.png

Thank you Peter, I just submitted a message with the login credentials

Ah gotcha - I got tricked by my own slug rewrite. Thank you Peter!!

If I just enter a User ID like 7 it works, but if I place the {{ author.ID }} variable it breaks the page. Does the {{ author.ID }} variable return anything else than the actual author user ID?