My favicon stopped working when I updated a couple versions ago and I haven't been able to fix it.
I tried following the codex's instructions as seen here, but I haven't had any luck. I copied the header.php from the parent theme into the child theme and made sure it was editable--but then the site wouldn't load--so I went back to square one. My header.php is only in the parent theme and I've added the following code after the
<head> but it's not working.
<link rel="shortcut icon" href="<?php echo get_stylesheet_directory_uri(); ?>/favicon.ico"
So far as I understand it, the reason for using a child theme is so that if your theme releases an update you don't lose everything you've changed, but if I'm willing to risk that... I should be able to edit the parent theme's header.php.