Products Not Found!

-- url of the page with the problem -- : www.uvgear.elements-chartreuse.co.uk/index.php/uvlights
-- HikaShop version -- : 2.6.3
-- Joomla version -- : 3.5.1

Following uploading an updated csv into Hikashop, I have suffered a number of problems

One if the issues is that some products when clicked generate a "Product Not Found" warning. This has occurred with about 20% of all products - so about 80 in total. Having read the forum, I noted that one way to deal with this is to change the canonical URL settings and also to switch off "Remove products and categories id in URLs". While the latter worked, It means that the product and category IDs are shown - which I do not want. So i need another way to resolve this.

I have also tried removing all the canonical URL's via mass actions, by choosing the product column "product_canonical", and then updating the values for that column by leaving the update box empty. This has not worked either as all of the canonical URL's are still present when I export a CSV. However, when I try the Mass action again - this time it shows that there are no product-_canonicals when I apply the mass action filter for the action! Have the canonicals been removed or not? Where am I going wrong?

Is there another way to solve the Product Not Found problem? An example of the problem is if you click on item 'UV960' at the top of the page attached.

Thanks