Why are these URL's suddenly appearing in WMT?

[ClickConsult]

One of our clients has suddenly experienced a sudden increase in crawl errors for smart phones overnight for pages which no longer exist and there are no links to these pages according to Google.

There is no evidence as to why Google would suddenly start to crawl these pages as they have not existed for over 5 years, but it does come after a new site design has been put live. Pages do not appear to be in the index when a site search is used.

There was a similar increase in crawl errors on desktop initially after the new site went live, but these quickly returned to normal. Mobile crawl errors only became apparent after this.

There are some URL's showing which have no linking page detected so we don't know where these URL's are being found. WMT states "Googlebot couldn't crawl this URL because it points to a non-existent page". Those that do have a linking page are showing an internal page which also doesn't exist so it can't possibly link to any page.

Any insight is appreciated.

Andy and Mark at Click Consult.

[DirkC]

If you recently did a site redesign - you probably deleted old redirect rules as well. Google seems to keep all the url's it has indexed over time stored somewhere - and the moment the old redirects disappear - you'll see these very old url's popping up in webmastertools. I had the same experience after a recent migration, and if you search on this forum, you'll find plenty of other people who have encountered the same thing.

Nothing to worry about - if these errors in WMT are annoying you could put the old redirect rules in place again, or if they are using a seperate folder structure, you could delete these folders via WMT. These errors will disappear over time, even if you don't do anything.

[RyanPurkey]

Hav you crawled your redesigned site with a tool like Xenu or ScreamingFrog?  That will help ferret out any bad links / 404 pages. Also, did you submit an updated sitemap with the redesign? Use 301s? Etc.

Edit: Looks like Dirk above hit on the most likely issue regarding 301s. You should be set with that.