Google's ranking algorithm has never been consistent, recently, I discover that the frequency of content updating on blog and website is getting more useful in increasing Google ranking as it uses to be. I think it started about a month ago.
The search term "make money online" is a good example to strengthen my point. If you often use this search term, you'll notice the websites listed in top 10 result fluctuate from time to time. The frequent fluctuations have lead to websites with decent number of backlinks that have stayed in first page for long period of time gradually one by one drop from top 5 to top 10 and from top 10 to top 20; and allowing more blog with frequent content update to get into top 10 listing. I have been in the niche of "make money online" for more than a year and never see it happens this way. It is obvious that Google has changed their ranking algorithm again and place more weight on content.
So if your website have experienced a drop in Google and you think that you have not done anything wrong. The frequency of content updating may be one of the main reasons. You may take a look at your competitors website to see whether they have started adding fresh content often. If yes, you may think about updating your site in on going basis as well. It will give you a better chance in re-gaining your Google ranking.