when we use "Use PHP to serve cache files.", the homepage is not cached. The cache file is generated, but it's not served, it just says "No wp-cache file exists. Must generate a new one." in the debug file.
I was looking into the plugin and found that the site permalink structure is first analyzed and if it ends with a slash, then only requests ending with slash are cached and vice versa. So if something does not obey the permalink rules, then it's not cached when using the PHP mode of serving cache. This is in in wp-cache-phase1.php.
The problem is, that our site uses permalink structure like /%year%/%monthnum%/%postname%.html which does not end with slash. So the wp-cache.php file sets wp_cache_slash_check to zero and that affects if the cached file is served in wp-cache-phase1.php. And since the homepage address ends with slash, it's not served from cached.
It's a weird issue, could you please have a look into fixing this?