Add to cart & Variant Error

6 0 1

Hi all, 

I found that my store has several error now. My customers should be able to choose variants on the page, but now they couldn't. The link below is one of the example. There should be M,L and XL size. It just show up with the price, but no variants are available.
Some of my products are sold out, but the add to cart button doesn't disappear. Instead, my customers are able to click add to cart button, and they will go to an error page. Please see the link below. Is the problems related to themes/ Apps? How can I solve the problems?
Thanks in advance.

Replies 2 (2)
Shopify Expert
293 17 23

@animes-pro   that product has variant your theme code may be broken so I will suggest restoring origin version from the main theme copy.

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6 0 1

I have tried to restore the original version of theme code, but it doesn't work. The problem still exists. Please tell me what else I can do now. Thanks.