Hi,
I suppose that you must have canonical URLs in your products and you must have the "force canonical URLs on listings" setting activated in the HikaShop configuration.
However, since the 2.1.3, which improved the construction of SEF URLs to remove the "show" part. And I think that's a combination of these which lead to your situation.
I would recommend to empty your canonical URLs with a mass action via the menu System>Mass actions, or change the "product SEF name" setting of the HikaShop configuration from "product" to "product/show" and it should then work again.