Back on 2/7, we changed CDNs from Amazon Cloudfront to StackPath for the images on our popular sports website. We ticked off the "use canonical headers" option when doing so. Starting on 2/12, we started to see crazy crawl stats in Google Search Console. On 2/17, our search traffic completely fell off. Starting on 2/17, we have been facing a 4-5 hour delay in our content hitting Google or Google News.
We then realized that between 2/12 and 2/19, our "indexed pages" in Google's search console shot up from 63,000 to 89,000. Over the next seven days, it continued up - to 98,000. I'm convinced that the sudden spike in indexed pages is the reason for the traffic drop and the delay. Between our articles, pages and category pages we should be around that 63,000 number.
When doing a site: search, Google only shows 58,500 pages. Bing shows 57,600. So I don't think we have duplicate content that I'd be able to find in the conventional way.
I've also parsed through the server log files. There aren't any weird URLs with
? type of parameters.
We have 45,000 images on our site. Is it possible that Google in now indexing those images and counting them in its "indexed pages" report? That's the only thing I can think of - but I've heard conflicting information about whether Google counts images in that number.