Soft 404 vs classic 404 errors - Which ones need immediate fixing?

Soft 404 vs classic 404 errors - Which ones need immediate fixing?

404 Errors 

404 errors are actually the responses codes in the browser for a web page that didn't load and basically, the content that had to be there isn't there anymore and your browser just tries accessing a dead end. 

There a lot of responses codes out there but the most important codes you need to get fixed are the ones in the 4xx range, better still the 404 errors! 
For proper SEO such errors don't need to exist, this is why it is really important to have zero 404s or to fix the ones that do appear. 

Keep in mind that Google constantly crawls your website and constantly checks external and internal links, all of them need to lead somewhere, but if you deleted a certain page and that page was already checked by a Google crawler, you got yourself a 404 error and it will be soon visible in Search Console. Also, if you ever linked internally to that page from another page, you also got an internal 404, meaning somewhere on your website a link points to a 404 which is bad user experience and Google doesn't see that as good indicators for ranks. 

So what exactly is a soft 404?

A soft 404 is not a response code like a classic 404 but in essence, does act pretty much the same. It is just a page without content in your website, the only difference being it doesn't return a response code.  Due to your bad website's structure, such pages can appear and although they aren't true 404 Google is smart enough to realize that it is wasting crawling budget on them, so it will go to mark them as soft 404 inside Search Console. 

What is their impact on SEO and how do we fix them?

Both soft 404 errors and normal 404 errors are bad for user experience, you aren't delivering to people that proper content in a proper manner, therefore don't expect much from search engines when it comes to ranking. So yeah, having a lot of 404 errors can affect your rankings and overall SEO. 

Clasic 404 errors can be found with crawling tools as Screaming Frog. 
Soft 404 have no response code so in essence won't be marked as 404 in Screaming Frog, even though a proper SEO can figure out soft 404 errors just by looking at the crawl pages. 

Soft 404 errors are only marked inside Search Console and marked as soft 404. Once you get such a list you should immediately fix them with the help of your developers if you lack the proper skills to fix them yourself. 
I also recommend implementing scheduled Screaming Frog crawls at least once a month to make sure you don't have a growing list of 404 errors.