Error with calculation of quantity in variations

I have a product with black and white color variation and the sales amount is 20 in 20. When using the category configured I get an error for the products with variation, when viewing the product the quantity shown is 20 but as it increases it does to 21,41,61 etc and decreasing it leads to 1, when the minimum configured was 20. It is important to indicate that it works perfect for simple products.

link with error: https://andesrank.com/cobronce/producto/enchufe-macho-convertible-ct-2/
correct link: https://andesrank.com/cobronce/producto/espuma-expansiva-500-grs-con-canula-rex/

both with the same category

The page I need help with: [log in to see the link]