I have plenty of duplicate titleshttp://example.com/?attachment_id=1678/feed/http://example.com/?attachment_id=1678/The first link triggers a 301 redirect to the second link. So why does Google Webmaster Tools interpret this as duplicate content and title?
Google Webmaster Tools: duplicate title even with a 301 redirect in place
google search console;duplicate content
GWT is known for not refreshing some parts of their data very often. Chances are your site got crawled before the 301's and what was reported at that time got stuck.Usually it will go away after a while but in some cases it will stay the same. I have about 40 error that haven't changed in over a year. All have 301's set on them.