Thanks for joining SITE_TITLE! You can now log into <a href="WEB_ROOT">SITE_TITLE</a> using the password you chose.
WEB_ROOT is not actually evaluated, so the link is broken.
I see that the email is generated in UserController.php #L236 (_sendConfirmedEmail). Oddly, editing that line to use the
$siteURL variable doesn't fix the issue (it results in an unlinked site title), even though the same approach works fine a few lines later (for the initial email, via _sendConfirmationEmail).