404_handler file is randomly deleted

Hey Frank,

We are having some random problems on our site when autoptimize is enabled. All the pages of our site are displaying fine but in some moments we have loading errors with broken css styles. Digging deep into the server I could see that the autoptimize_404_handler.php file located in wp-content is suddenly deleted and takes a few seconds to recreate itself. This is happening every few minutes and does not follow any logic, at least I have not found it.
What could be forcing this file to constantly delete and recreate itself?

We are testing with the latest stable version 2.9.5.1 and have also tested with beta 3.0.0-beta-4 with identical results. 404 fallbacks option is enabled in the settings page. We also have W3-Total-Cache activated but this is happening even with this cache plugin deactivated.

Our webserver is NGINX and we have the rewrite rules in place, as you suggested in AO FAQ page:

location ~* /wp-content/cache/autoptimize/.*\.(js|css)$ {
    try_files $uri $uri/ /wp-content/autoptimize_404_handler.php;
}

Any idea what might be going on? Thank you in advance