Ranking dropped for 2 main keywords, should be a simple fix

[Ruby707]

I haven't been here for awhile, good to see some old faces. I used to read all the top rep members' posts.

Anyway, here's the issue, I have a website and the home page ranked 116th and 28th for my two main keywords pre-SEO work (May 2015).
Then, last month the same two main keywords ranked 10th and 4th.
Today, the two keywords rank 129th and 113th. Plus for one of the keywords, instead of the home page ranking, an internal case study page is now ranking instead.

I have no idea why the rankings have gone down. I've done SEO for many sites over the years and very rarely had this problem.

As far as I'm aware, I've done everything by the book on-page and sourced what I know are quality links and citations, that's all I've changed and my approach usually works fine.

If you need more info I'll happily supply it.
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