Add to cart button is hidden

Hi,

You have the "synchronize add to cart" setting activated under the Cart section of the Main tab of the HikaShop configuration.
In that case, the quantity input/add to cart area is synchronized with the cart so that when you have 2 elements in the cart, you see a 2 in the quantity input field of the product and if you increment/decrement it, it directly updates the quantity in the cart.
This is quite useful on websites with many products where users are expected to purchase many products in each order (like on a grocery "drive" website).
In your case, you just want to turn off that setting to have a more standard behavior.