What is a Soft 404 error?
Usually, when a visitor requests a page on your site that doesn’t exist, a web server returns a 404 (not found) error. This HTTP response code clearly tells both browsers and search engines that the page doesn’t exist. As a result, the content of the page (if any) won’t be crawled or indexed by search engines.
A soft 404 occurs when your server returns a real page for a URL that doesn't actually exist on your site. This usually happens when your server handles faulty or non-existent URLs as "OK," and redirects the user to a valid page like the home page or a "custom" 404 page.
This is a problem because search engines might spend much of their time crawling and indexing non-existent, often duplicative URLs on your site. This can negatively impact your site's crawl coverage because your real, unique URLs might not be discovered as quickly or visited as frequently due to the time Googlebot spends on non-existent pages.
How to deal with Soft 404 Errors
We recommend that you configure your server to always return either a 404 (Not found) or a 410 (Gone) response code in response to a request for a non-existing page. You can improve your visitors' experience by setting up a custom 404 page when returning a 404 response code. For example, you could create a page containing a list of your most popular pages, or a link to your home page, or a feedback link. But it's important to remember that it’s not enough to just create a page that displays a 404 message. You also need to return the correct 404 or 410 HTTP response code.