My websites are hosted on a different IP from the server's IP address. After updating from 5.3.8 to 5.4 none of the websites load. This was in the apache error log:
[/etc/apache2/conf/httpd.conf:188542] Listener for 12.34.56.789:443 is not available!
[/etc/apache2/conf/httpd.conf:188542]...