Yes, for example, If there are 2 products in a category, I can view both, but If there is only 1 in that category, I can't view the product page.
Here is an example link, this is a product listing page for a category, you can see 1 product which is not working on product page.
Here you can check:
Category listing page:
novi.com.tr/ikinci-el
Product listing page:
novi.com.tr/ikinci-el/ruzgar-turbini
Product page:
novi.com.tr/ikinci-el/ruzgar-turbini/uru...ar-turbini-ikinci-el
(which is not working)
If I duplicate this product or create a new one, I can view both product pages without problem. As I said before, If I login on website, I can view the product page, even If there is still only 1 product.
About canonical URLs, You know, normally you can view a product with different URLs If you go to URL directly, For example:
Default (true) path:
novi.com.tr/guc-sistemleri/jenerator/diz...10-4-3-faz-jenerator
Wrong path:
novi.com.tr/endustriyel/forklift/dizel-j...10-4-3-faz-jenerator
Because of this wrong directory link, we see wrong widgets like side menu. thats all.
With canonical URLs, If you mean giving links rel="canonical" tag, No I didn't.
I can give more specific details If you need, or I can create a user..