Image URL Change Catastrophe

[wantering]

We have a site with over 3mm pages indexed, and an XML sitemap with over 12mm images (312k indexed at peak). Last week our traffic dropped off a cliff.

The only major change we made to the site in that time period was adding a DNS record for all of our images that moved them from a SoftLayer Object Storage domain to a subdomain of our site. The old URLs still work, but we changed all the links from across our site to the new subdomain. The big mistake we made was that we didn't update our XML sitemap to the new URLs until almost a week after the switch (totally forgot that they were served from a process with a different config file). We believe this was the cause of the issue because:

• The pages that dropped in traffic were the ones where the images moved, while other pages stayed more or less the same. We have some sections of our property where the images are, and have always been, hosted by Amazon and their rankings didn't crater. Same with pages that do not have images in the XML sitemap (like list pages).
• There wasn't a change in geographic breakdown of our traffic, which we looked at because the timing was around the same time as Pigeon.
• There were no warnings or messages in Webmaster Tools, to indicate a manual action around something unrelated.
• The number of images indexed in our sitemap according Webmaster Tools dropped from 312k to 10k over the past week.
• The gap between the change and the drop was 5 days. It takes Google >10 to crawl our entire site, so the timing seems plausible.

Of course, it could be something totally unrelated and just coincidence, but we can't come up with any other plausible theory that makes sense given the timing and pages affected.

The XML sitemap was updated last Thursday, and we resubmitted it to Google, but still no real change. Anyone had a similar experience? Any way to expedite the climb back to normal traffic levels?

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[KeriMorgret]

Just checking to make sure that there aren't any problems with the analytics code itself. Have you made sure that tracking is still on all the pages? If you have access to server log files, like awstats, do you see the same drop?

[wantering]

The drop also appears in Webmaster Tools, including a commensurate drop in Impressions.