There are 404 pages with two kinds of
response headers (copypasted in full length from Chrome DevTools, Network tab):
cache-control:max-age=0, no-store content-type:text/html date:Wed, 24 Jan 2018 10:55:59 GMT server:Apache/2.4.29 (Ubuntu) status:404 x-powered-by:PHP/5.5.9-1ubuntu4.22
cache-control:max-age=0, no-store cache-control:no-cache, max-age=0, must-revalidate content-type:text/html; charset="utf-8" date:Wed, 24 Jan 2018 10:55:40 GMT expires:Thu, 19 Nov 1981 08:52:00 GMT pragma:no-cache server:Apache/2.4.29 (Ubuntu) set-cookie:bypassStaticCache=deleted; expires=Thu, 01-Jan-1970 00:00:01 GMT; Max-Age=0; path=/; httponly set-cookie:bypassStaticCache=deleted; expires=Thu, 01-Jan-1970 00:00:01 GMT; Max-Age=0; path=/; httponly status:404 x-powered-by:PHP/5.5.9-1ubuntu4.22
The pages with the first kind of
response headers aren't recognized by Google as 404. Instead of 404 alerts the Search Console those pages as duplicate pages without canonical tag.
The pages with the second kind of
response headers are correctly recognized as 404.
Not recognized means: Google calls such pages Duplicate page without canonical tag, despite the fact, that developer tools of Firefox and Chrome get correct 404 status code.
Why is it so? What prevents the correct status code recognition? Does the answer need additional information? Just say - i'll try to provide it.
PS: maybe it is a bug of the new Search Console...? @JohnMu