Random unexpected E_WARNING on file_exists() php function

Hi everyone, I’m using Grav in production for months and sometimes the site goes down with the following E_WARNING.

Why is this occurring and how can I fix this issue? I’ve set up dir and file permissions.. I have to restart apache to make it run again.

Does it have something to deal with file / dir permissions? My app is running under ww-data user and web group (including www-data and deploy user).

Thank you

Are you adding files via FTP? If so they are probably owned by a user other than www-data and causing the problem

I'm adding files pulling from git from the VPS, I've setup a git hook that fix permissions after pull / merge and I've created a setup.php that performs an unmask before each request as stated in the permissions section of the official doc.

This happens randomly and I have to restart apache.

I'm on Ubuntu 15.04 VPS with PHP 5.6.4-4ubuntu6.4 and Grav version v1.4.3

Is Grav expecting a languages dir in the root of active theme? I've added it

Got again the same error.. I need to restart apache each time