Errors on your website are generally a bad thing – and while Google has always said that website errors aren’t a good thing – they’ve never specifically stated that those errors will play any role in your website’s crawl & indexing rates. However a recent question has gotten confirmation that 5xx errors will cause a slow down in your website’s crawling rate. Which makes sense – because Google doesn’t want to serve up website pages that don’t work.
Check out the full response from Google’s John Mueller below:
That's a very vague question, and a post from 2016, it makes it a bit hard to guess :). We do crawl old 404 pages from time to time, that's nothing to worry about. It's more problematic if they're 5xx errors (we slow crawling), or if the URLs were meant to be indexed.
— John ?.o(???)o.? (@JohnMu) July 9, 2018
Read on for more Google confirmations here.