The urlRecord table doesn't have any links in it. If anyone can tell me where nopCommerce stores product links, that would probably fix the problem.
I am having the same issue. I imported all of my products with an Excel file.
None of the product links work. The category links work OK. Like you said, if I go to a product edit and save it, then the link works fine on the public store.
If I put a product sku into the search box, it finds it, but when I click on it, it gives a "Page not found" error an the address bar shows "http://localhost:15536/null"
My UrlRecord table has 120 entries in it.
If you have resolved this issue, I would like to hear about it. Otherwise, if I come up with a resolution I will post it here.