I have a client whose site often contains a category (and sometimes additional sub-categories) and a product with the same name and URL key, which I am aware is unusual.
They recently complained that they were getting "URL key already exists errors" when setting up a new category and assigning products.
I assumed initially that this was just because the URL key needs to be unique, and could see why that would be the case. However, looking at the site, they have been able to do similar, if not the same, in the past. When URL conflicts have happened, Magento tends to just append a number to the URL in order to differentiate.
I tried un-assigning and re-assigning one such product to the same category, and I was unable to do so because the duplicate URL warning then appeared.
Whilst my advice will be to always use unique keys from now on, I was wondering if there have been any changes in how Magento tests for conflicts with URL keys when assigning a product to a category or creating a sub-category?
The site was Magento 1 (and most of the products created on that), and so I wondered if perhaps it could just be a change in how Magento 2 does things? They have never used SEO extensions which could impact on this area.