This warning is popping up in my logs:

stderr: "PHP message: PHP Warning: Undefined array key "host" in /wp-content/plugins/powered-cache/includes/utils.php on line 938"

It looks like the code assumes this exists and I'm not sure if any of the parsed url components are guaranteed to exist.

I've patched mine with

938 $sub_dir = isset($url_info['host']) ? $url_info['host'] : '' ;

if ( isset($url_info['path']) && ! empty( $url_info['path'] ) ) {

Hope this helps.