Think I might have found it.

Try altering includes/functions/extra_functions/functions_bmz_image_handler.php
about line 114 from
Code:
function handle_image($src, $alt, $width, $height, $parameters)
{
    global $ihConf;

    if ($ihConf['resize']) { //Image Handler processing is enabled
to
Code:
function handle_image($src, $alt, $width, $height, $parameters)
{
    global $ihConf;
    $image_ext = strtolower(pathinfo($src, PATHINFO_EXTENSION));
    if ($ihConf['resize'] && ($image_ext != 'webp')) { //Image Handler processing is enabled