Stretched images

Hi,
since some days ago the images that pop-ups of the product page look stretched vertically. The thumbnails work fine.

You can see an example here: https://bit.ly/1yRiw2w

The only thing I’ve done was installing WonderPlugin Slider. I tried to disable it, but has not solved the problem.

Any advice?

Thanks in advance.

https://www.ads-software.com/plugins/woocommerce/