It appears you may have changed some products' Item Numbers without recopy-pasting fresh button codes to sell those products -- e.g., your first link above references &i=HS-615 (this indicates that Add to Cart button/link is for Item Number HS-615), but you have no product with that exact Item Number at present (though you do have HS615, no dash).
Most product settings do not affect the button code, so any existing buttons already in your site would pick up those changes automatically. However, since the Add to Cart button URL references the product's current Item Number, changing that requires you to update the button code in your site accordingly. The only other settings which affect the button code would be changes to "Variations describing item options" or "Variants affecting item SKU/price/weight/stock", or changing the Min./Suggested Prices for items which "Let buyer edit price".
