Add to cart button changed to out of stock in the product page (out of stock products)

Here is a link to one of my product that are sold. https://mayagallery.ca/product/kuru-2-4-x-4-8/ I'm not sure why but the add-to-cart buttons for the related products also changed to sold. I think there is a CSS that cause this problem, but I could not find any. Can someone help me please to fix this issue? Thank you

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