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I'm turning to the Moz Community because we're completely stumped. I actually work at a digital agency, our specialism being SEO. We've dealt with Google penalties before and have always found it fairly easy to identify the source the problem when someone comes to us with a sudden keyword/traffic drop. I'll briefly outline what we've experienced: We took on a client looking for SEO a few months ago. They had an OK site, with a small but high quality and natural link profile, but very little organic visibility. The client is an IT consultancy based in London, so there's a lot of competition for their keywords. All technical issues on the site were addressed, pages were carefully keyword targeted (obviously not in a spammy way) and on-site content, such as services pages, which were quite thin, were enriched with more user focused content. Interesting, shareable content was starting to be created and some basic outreach work had started. Things were starting to pick up. The site started showing and growing for some very relevant keywords in Google, a good range and at different levels (mostly sitting around page 3-4) depending on competition. Local keywords, particularly, were doing well, with a good number sitting on page 1-2. The keywords were starting to deliver a gentle stream of relevant traffic and user behaviour on-site looked good. Then, as of the 28th September 2015, it all went wrong. Our client's site virtually dropped from existence as far as Google was concerned. They literally lost all of their keywords. Our client even dropped hundreds of places for their own brand name. They also lost all rankings for super low competition, non-business terms they were ranking for. So, there's the problem. The keywords have not shown any sign of recovery at all yet and we're, understandably, panicking. The worst thing is that we can't identify what has caused this catastrophic drop. It looks like a Google penalty, but there's nothing we can find that would cause it. There are no messages or warnings in GWT. The link profile is small but high quality. When we started the content was a bit on the thin side, but this doesn't really look like a Panda penalty, and seems far too severe. The site is technically sound. There is no duplicate content issues or plaigarised content. The site is being indexed fine. Moz gives the site a spam score of 1 (our of 11 (i think that's right)). The site is on an ok server, which hasn't been blacklisted or anything. We've tried everything we can to identify a problem. And that's where you guys come in. Any ideas? Anyone seen anything similar around the same time? Unfortunately, we can't share our clients' site's name/URL, but feel free to ask any questions you want and we'll do our best to provide info.