lucy24, I've lengthened your title for clarity, adding
"Surge in Redirected requests" to your ingenious and amusing title:
"Google finds an old shopping list".
Your shopping list comment is a metaphor for how Google sometimes crawls old data, but search engines don't do well with metaphors (and often people don't either). I'm thinking that your question wasn't about the usual 404 error question, but it was rather specifically about Redirected requests and Google crawling, looking back over a good many years. Thus, the addition.
In the past I've felt that such massive Google reviews of old legacy data were a sign that Google was doing something for which it eventually wanted a "clean" url list, like perhaps an update, and we've discussed that in two threads I'm citing below...
Massive jumps in GSC legacy crawl errors - who sees this? 9/8/2016 https://www.webmasterworld.com/google/4817870.htm [webmasterworld.com]
17 May 2013 - GWT Sudden Surge in Crawl Errors for Pages Removed 2 Years Ago? https://www.webmasterworld.com/google/4575982.htm [webmasterworld.com]
Note that during the progress of the 2016 thread, Simon_H, who'd started it, joined the Sep 9, 2016 Google Hangout to ask John Mueller about the crawl errors we were discussing, and the exchange was reported that day by Barry on SERoundtable...
Google: The Increase In Crawl Errors Are Nothing To Worry About; Just Hungry Crawlers Sep 9, 2016 - by Barry Schwartz https://www.seroundtable.com/google-increase-in-crawl-errors-22669.html [seroundtable.com]
To quote Barry at greater length than I normally would, Barry's article cites our thread about which Simon was asking...
Over the past week or so, some webmasters have been reporting an increase in crawl errors. It is mostly documented in this WebmasterWorld thread.
Some suspect it has to do with an algorithm update - but we've covered not just once but twice that these crawl changes in Google Search Console have no relation to upcoming algorithm updates - at least that is what Google told us.
John Mueller was asked about this by Simon in the Google Hangout.... John essentially said that he looked into some of these reports and yes, it is unrelated to any algorithm thing....
Simon later that day posted in our thread...
I'm not convinced this is just coincidence. From a statistical point of view, having multiple sites flagging massive jumps in crawl errors around the same time (we're actually receiving warning emails from GSC it's so severe) is unlikely to be pure coincidence, plus the last time people saw this happen, Penguin 2 hit a week later.
He posted a comment to the same effect on SER.
I should add that, following the discussions above, on Sept 13, 2016, that MOZcast reported the largest changes it had ever recorded up to that date; and Penguin 4.0 was announced on Sept 23, and rolled out slowly over subsequent weeks. In retrospect, there appears to have been a degree of nested updates. Here, for reference, is the WebmasterWorld thread on Penguin 4.0....
Penguin: Core, realtime and updated today Sept 23, 2016 [
webmasterworld.com...]
So, back to the OP here...
Does Google randomly cycle through websites, pulling up old redirects every few years when it gets to be your turn? Or are they working on some new algorithm?
I'd vote for the algorithm, but I'm sure Google won't confirm that, and it may also be that Google cycles through websites, but I don't know about how "random" the datasets are. It may also be that on some of the cycles John looked at, there was no update pending, or at least no update pending which required a clean list or index, and therefore no old data (aka shopping list) was being used. Clear? ;)
It's interesting to me that you're seeing Redirected request errors instead of 404 errors, suggesting that Google might be looking at yet a different kind of update, albeit I'm not sure what that might be.
I'm thinking there might be further clues in some of your observations, which suggest perhaps that some issues might be getting checked out which could involve an update which is recursive and which involves a different area of the index, as in one that involves prior redirects. (Note that this is conjecture, and that I'm not a Google search engineer.)
