Pretty Photo Lightbox Stretching Images on Tablet

Hello,

I am running Highend Theme 3.5.1.3 on WordPress 5.1.1.

After the last WP update, lightbox images in my Pretty Photo gallery are stretched to fill the screen width when viewed on tablet. The images are not Retina optimized and do not look good when they are enlarged like this.

The images look good on desktop and mobile (iPhone), but they look too big on tablet (iPad).

How can I stop Pretty Photo from enlarging the lightbox images on iPad? I would like the images to look the same size on tablet as they do on desktop.

Thanks.