Hi, I had problems with my categories archive - pages 2 and onwards came back with 404 errors. Having not found the solution on any existing support forums, I managed to stumble upon it in the Yoast SEO Plugin.
Under the permalink settings tab in his plugin, there exists an option 'strip the category base (usually /category/) from the category url'.
If you enable this, your site will no longer get confused with the 2 different locations of category archives it had.
This, in my opinion, provides a logical, reliable and permanent fix to the problem many forums have debated over.