Yakovos Frountas

I can confirm this bug in the latest version.

In order to fix the error of the filesize(): stat failed for you can alter the file BiggerThanSource.php with the following code until an official fix is released

<?php

/*

This class is made to not be dependent on WordPress functions and must be kept like that.

It is used by webp-on-demand.php. It is also used for bulk conversion.

*/

namespace WebPExpress;

class BiggerThanSource

{

    /**

     * Check if webp is bigger than original.

     *

     * @return boolean|null   True if it is bigger than original, false if not. NULL if it cannot be determined

     */

    public static function bigger($source, $destination)

    {

        if (!file_exists($source) || !file_exists($destination)) {

            return null;

        }

        $filesizeDestination = @filesize($destination);

        $filesizeSource = @filesize($source);

        // sizes are FALSE on failure (ie if file does not exists)

        if (($filesizeDestination === false) || ($filesizeSource === false)) {

            return null;

        }

        return ($filesizeDestination > $filesizeSource);

    }

}

also if you are getting a warning on the file PictureTags.php change the line 142 from

@$dom->loadHTML($html);

to

@$dom->loadHTML($html, LIBXML_NOWARNING | LIBXML_NOERROR);

hope that helps a bit.