@Serg:
Just a quick question.
What happens when I update the theme.
Currently I am using Child Theme.
Regards.

Dear Serg:
Thanks for your reply and immense help…but

Because this product has duplicate featured image in the gallery. Just open two products in admin panel and compare how products are added to them.

Thanks I understood this.

We suggest you change a number of thumbnails per slide in the file xstore/woocommerce/single-product/product-thumbnails.php from 4 to 10. Find this code

No it is not working / not happening even after changing 4 to 10.

http://prnt.sc/duarqf

I cleared Chache user different computer but no help.
Please let me know if you need ftp access.

regards.

Update.
1. I removed product featured imaged and whole gallery was stopped working.
Here the link for a demo product without featured image.
http://customjackets.apps-1and1.net/shop/made-to-order/made-to-order-mens/xstore-demo/

2. Even after remove that css snippet it showing the same error.

Please solve my problem

Thanks.