I use wp_logout_url() to output a logout link. How can I avoid displaying the confirmation page that appears after clicking the link?

<a href="<?= wp_logout_url(get_permalink()); ?>">Log out</a>

Why does this even happen? I already did some googling and it seems to have something to do with a missing nonce but in my case the nonce isn't missing at all. wp_logout_url() adds the nonce to the link.

edit:

I have figured out now that if I log in with the standard WordPress /wp-admin/ login form, logging out works without the confirmation page. But if I use my own custom frontend login form that uses wp_signon(), logging out only works with the confirmation page.

Here is my login code:

add_action('after_setup_theme', 'my_login');
function my_login()
{
  if(!empty($_POST['my_username']) && !empty($_POST['my_password']))
  {
    $user = wp_signon([
      'user_login' => $_POST['my_username'],
      'user_password' => $_POST['my_password'],
      'remember' => true],
      is_ssl());
    if(is_wp_error($user))
    {
      echo $user->get_error_message();
    }
    else
    {
      wp_set_current_user($user->ID);
    }
  }
}

The form on the frontend simply is:

<form method="post" action="<?= get_permalink(); ?>">
  <p><input type="text" name="my_username" placeholder="Username" /></p>
  <p><input type="password" name="my_password" placeholder="Password" /></p>
  <p><input type="submit" name="submit" value="Login" /></p>
</form>

Am I doing something wrong here which causes this to behave differently to the normal WordPress login?