Hello,
I have disabled Variation gallery in Theme Options > WooCommerce > SIngle product Variation gallery. Sometimes it caused the mentioned issue. But not in your case.
I checked your product https://www.kartmor.com/product/casio-m110-gold/?v=fb1c5b0d2f97 and checked the wrong images. I see that image does not display the correct preview even with the default theme https://recordit.co/4tyImZORoM Not sure why this happens. I added a filter to your child theme to display medium image size in the product gallery instead of the shop thumbnail and it loads the same image that is uploaded in the product settings. But I would recommend you to contact WordPress support to find out why your media displays wrong thumbnails in general.
Did you use any tools for image optimization on your site? Or any kind of server cache?
Regards