Gallery freezes when opening some picture

WD Photo Gallery plugin stopped working after upgrade. When I click on some picture in a gallery the gallery tries to load something and there is infinite loading progress message.

I have found this in Chrome Console:

XMLHttpRequest cannot load https://www.literak.cz/wp-admin/admin-ajax.php?action=GalleryBox&tags=0&cur…watermark_type=none&slideshow_effect_duration=1&image_id=46&filter_tag_0=0. Request header field X-Requested-With is not allowed by Access-Control-Allow-Headers in preflight response.

Example: https://www.literak.cz/2017/04/lodi-po-zapadnim-stredomori/