Several month ago, i saw Google Cache 404s error and that google cache problem coming after mobile first indexing update.

 
John Mueller from Google said about this Google caching issues on twitter that you don’t have to  worry about it. Sometimes it takes time and doesn’t affect crawling, indexing and ranking.

Now above issue completly resolved. Here is what Glenn Gabe said on twitter. I also tested to my blog and i found caching issue resolved.

So we dont have to use Google Cache 404 Hack. Many webmasters used these hacks for checking google last cache.