helix ultimate add to cart problem

Hi,

Thanks for the clear report, that's very helpful. The fact that it works on Cassiopeia but not on Helix Ultimate is the key: it points to a view override that exists only in your Helix Ultimate template, not to a HikaShop bug.

I had a look at your product pages and confirmed it. Your product page is being rendered by an old override of the HikaShop product view, sitting in:

templates/shaper_helixultimate/html/com_hikashop/product/

That override is from before the 6.5.0 product page rework. In 6.5.0 we removed the single form element that used to wrap the whole product page, and each variant now has its own form so that adding a variant to the cart submits only that variant.

Your old override still wraps every variant in one shared form (named hikashop_product_form), and that single form contains one hidden product_id field per variant. When you click "Add to cart", the browser submits all of them and only the last one is kept, which is why the last variant in the list is always added no matter which one you select.

Fix: bring that product page override up to date, or simply remove it if you don't have custom changes you need to keep.

- Easiest: in HikaShop go to Display > Views, look for the overridden product views (they are flagged), and use the "Compare/diff with original" button to see your changes. If there is nothing custom you need, delete the override so HikaShop uses the current 6.5.0 layout.
- If you do have customizations, re-apply them on top of the new 6.5.0 product templates rather than keeping the old files, since the old form structure is no longer compatible.

The override only affects Helix because Joomla template overrides live inside the template's html folder, which is exactly why Cassiopeia is unaffected. Once the product view override is removed or updated, variant selection and add to cart will work the same under Helix Ultimate.
If the override comes from your template provider, then you might want to contact their support in order to report the issue.