get_posts gives different result than wpdb->get_results

I ran into something that has me completely stumped. For a cron job I need to retrieve which users are ‘marked’ as VIP and then retrieve the posts from these VIP users.

global $wpdb;
$capabilities_field_name = $wpdb->prefix . 'capabilities';
$user_args = [
    'meta_query' =>
        [
            'relation' => 'OR',
            [
                'key'     => $capabilities_field_name,
                'value'   => '"independent_pro"',
                'compare' => 'LIKE',
            ],
            [
                'key'     => $capabilities_field_name,
                'value'   => 'agency_pro',
                'compare' => 'LIKE',
            ],
        ],
    'fields' => 'ID',
    'number' => 999, // to select all users
    'exclude' => [1], // admin user
];

$user_query = new WP_User_Query( $user_args ); 
$pro_users  = $user_query->get_results();
// $pro_users = array with 2 user ids: 21 and 44

if ( count( $pro_users ) > 0 ) {
    $pro_users = implode( ',', $pro_users ); 
    $pro_ads   = get_posts( array(
        'post_type'   => PostTypes::PROFILE,
        'number'      => -1,
        'author'      => $pro_users, 
        'post_status' => [ 'publish', 'pending' ],
    ) );
    // result = 5 posts (which is incorrect)

    $pro_users = implode( ',', $pro_users );
    $pro_ads   = get_posts( array(
        'post_type'   => PostTypes::PROFILE,
        'number'      => -1,
        'author'      => 21
        'post_status' => [ 'publish', 'pending' ],
    ) );
    // result = 2 posts (which is correct)

    $pro_users = implode( ',', $pro_users );
    $pro_ads   = get_posts( array(
        'post_type'   => PostTypes::PROFILE,
        'number'      => -1,
        'author'      => 44
        'post_status' => [ 'publish', 'pending' ],
    ) );
    // result = 4 posts (which is correct)

    $pro_ads = $wpdb->get_results(
        "
            SELECT * 
            FROM $wpdb->posts
            WHERE post_status IN ('publish','pending') 
                AND post_type="profile" 
                AND post_author IN ({$pro_users}) 
            LIMIT 1000
            "
    );
    // result = 6 posts (which is correct)
}

Yes, I deactivated all plugins and I switched back to twentysventeen to test it… No change.
No errors in console or log either.

Why is it always that I look for a solution for hours… then post it here and within a few minutes I find the solution myself….

I found the solution in this post.

The default arguments for get_posts() function include ‘numberposts’ => 5.

So when I set number, it was ignored and 5 was set for numberposts. The correct values are posts_per_page and numberposts (imo a poorly chosen variable).