Google is consistently updating their search algorithms so rankings fluctuating on a daily or weekly basis is pretty normal. I get this question often so here are some of the most common reasons I’ve seen for a sudden drop in rankings:
A site with solid traffic has changed key elements of their code or have gone through a redesign. Any structural changes to a website – even if you keep all content in place – will have an impact on your rankings.
Migrating hosts, changing domains, or changing CMS systems can have drastic impacts on organic rankings. I highly recommend you consult an expert before you migrate to make sure to mitigate as much damage as possible.
All those backlinks you built back in 2012 have finally caught up with you. If you used black-hat or spammy strategies to build links back in the early days of SEO, Google can levy a manual penalty on your site and drop your rankings.
A serious competitor has emerged on the market. For some niches, even poorly optimized sites can rank well for a long time, but if a national or local competitor emerges on the market, your rankings can drop.
You’re preventing search engines from accessing your site. Subtle changes to key documents on your site can essentially blacklist your site from organic rankings. Learn about how to leverage a robots.txt file and make sure your site is ready for indexing from a technical standpoint.
You took down content you thought was useless, but it was actually driving lots of traffic. All to often, I see site owners cutting pages willy-nilly without any regard for how it might impact their rankings.
You have a lot of new 404s on your site. 404s are an indication that a site is not very useful or well-maintained. An influx of 404s can have a negative impact on your site’s SEO, especially for smaller websites.
A competitor is actively spamming you. I’ve seen if before. Sometimes competition can make people do nasty things and organic subterfuge is very much a thing. Keep an eye on your backlinks and your online reputation.