PHP warning on switch_to_olduser

This happens on action ‘switch_to_olduser’

ErrorException: Warning: Trying to access array offset on value of type bool
#8 /wp-content/plugins/user-switching/user-switching.php(128): user_switching::remember
[…]

The relevant code starting at line 124.

$current     = wp_parse_auth_cookie( '', 'logged_in' );

// Here we calculate the expiration length of the current auth cookie and compare it to the default expiration.
// If it's greater than this, then we know the user checked 'Remember Me' when they logged in.
return ( ( $current['expiration'] - time() ) > $cookie_life );

The function wp_parse_auth_cookie can return a (bool) false. Then you can’t do an array lookup. Replacing return with return $current && should do the trick.