Nope - I installed autoptimize on one site and that made some improvements, though ideally the two programs could run together.

Same issue here as well. The website must have run some automatic updates, just got a message today that it's crashed due to the following error:

An error of type E_ERROR was caused in line 452 of the file /xxxx/xxxx/public_html/wp-content/plugins/w3-total-cache/Cache_File.php. Error message: Illegal length modifier specified 'f' in s[np]printf call

I am unable to log in via the admin panel and will follow steps to remove the plugin and files via FTP.