Hi,
1. If you can't find the folder, then it would mean that it doesn't come from a template override but something else.
We'll have to look at the problem directly.
Could you provide a link to a product page with the problem ? I tried to check the link you provided with your first message, but it works fine there and I can see that you're using the 2.6.2 there.
2. HikaShop 2.6.4 has been released months ago. If that problem was experienced by everyone upgrading to the 2.6.4, we would have fixed it long ago. In fact such display problems sometimes occur with view modifications, but it doesn't seem the be the case on your website. So it's the first time I see that display problem not coming from a view override. Hence it's only related to your website. Once the source of the problem is identified and fixed, there is no reason you would get the same problem next time you update.