Browser stacks different versions of style.css

The problem comes from that the parent style is loaded twice :

  1. one with version (‘?ver=1.0 etc, first on your picture and loaded by your parent theme with versionning on wp_enqueue_style ),
  2. another without (the second on your picture, called by your function php).

To solve this : remove

wp_enqueue_style( $parent_style, get_template_directory_uri() . '/style.css' );

As it is already loaded by your parent theme and described as a dependency of your child style.