Google’s webmaster trends analyst John Mueller has confirmed on Twitter that there is a reporting glitch with the crawl stats “time spent downloading a page” report in the Google Search Console for the dates February 20 and 21.
There was a massive dip in the number being reported on those two days, but that dip was just a glitch in the reporting. It does not reflect actual crawling or search rankings.
Here is a screen shot that illustrates the glitch:
Mueller wrote:
Here is the tweet:
https://twitter.com/JohnMu/status/968046819723882496
