Could be that PHP doesn't have the write to delete the files... but I'm not sure because, php wouldn't have the right to create them either... Maybe CouldFlare yeah....
Ok but we are talking about a cache provider that is causing problems, not Chevereto. If you use Cloudflare (basic) you will notice that the cache and the purge are slow. Sadly, Cloudflare can't be tuned by php or something that we can trigger from the script.