Hi!
hikashop 2.4.0
joomla 3.4
I had the same problem, if in hika configuration---> SEF url options---->Remove products and categories id in URLs---> set YES
On front end product listing was fine, but when click on product link (try to get product page) i had error message "Product not found"
Problem is only when importing product data from csv or ect. I check the database and figure out, the problem coming from product_alias...it was empty. Alias automatic filling was set "YES"
When you import products from csv, product_alias will NOT filling automatic, that cause the problem.
Solutions
1. Turn off (set NO) "Remove products and categories id in URLs " in configuration on page SEF url otions.
2. In your csv file give a column with name "product_alias" and fill with data.
3. Imort your csv--->open the product in administartor--->simple save it without change anything (when you save the product hikasop is auto fill product_alias if this option is set on)---and done.
Or maybe Developers take this on "to do list" and product import will fill autamaticly the product_alias column.
Hikashop is one of the best shop systems, and always will better and better, thank's for it!