Hi,
Are you sure that you do not have some view overrides ?
When I take a look at the product page, I can see an "add to cart" button but that's not the official HikaShop code ; so I think that you have some overrides which are not fully compatible with the product listing.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.