The complaint came around for months on end that Google Cache is giving a 404 error for certain websites. The matter of concern in this regard is that, it means that there is some problem with those websites and so, their rankings in Google will go down. Though there is nothing much to be worried about, the website owners are still getting anxious and worried.
Google mentioned that getting a 404 cache does not impact the rankings and many of the sites are getting 404 caches after they made the move to mobile first indexing procedure. Thus, this is a common scenario.
Google’s John Mueller posted on Twitter about a workaround that many of the SEOs have been discussing for quite a while now. If the URL of the cache URL is changed, then you can resolve the problem easily. You can remove the URL and replace it with x.xyz/ and it will start working. But you need to click on 404 caches URL at first and then try to change it.
The sites that are yet to move to mobile indexing have no problem with their cache URL. However, this is a issue that Google knows about and has assured the websites that there is nothing to worry.