Google may be crawling sites more and harder over the past several days. The WebmasterWorld forums has several SEOs saying they are seeing significant spikes in crawl rates by GoogleBot.

Also, I checked dozens of sites in the old Google Search Console, to see the crawl stats and most, not all, but most, have a significant spike in crawling.

Here is one of many screen shots from the crawl stats section within Google Search Console:

Here are some of the comments from WebmasterWorld:

Have you noticed large spikes in crawling? Note, Google has said crawl spikes do not mean algorithm updates are about to happen.

Forum discussion at WebmasterWorld.