Discussion of that patent on WebmasterWorld is here.... Google's Rank Modifying Patent for Spam Detection Aug 18, 2012 https://www.webmasterworld.com/google/4486158.htm
You don't mention what kinds of queries dropped you to #55, whether this was one query or several. Possibly you just diluted or skewed the focus of your original targeting. What you describe sounds like the title looked to Google like it might have been stuffed with keywords. Or possibly the site has now aged enough that you're no longer in the "honeymoon period", which Google gives when a site is first put up, which provides an initial ranking boost.
I should ask, btw, whether this is the same site as the site we were just discussing in this thread. [webmasterworld.com
...] ....about multiple related sites on the same server. I ask both because, in that thread, you describe a lot of changes made on the site... and because you say that the site has no backlinks.....
I wish I had the time to do SEO on all the sites, I did however change up the content, replaced old design with HTML5 responsive and they are still sitting on 5th page. No backlinks.
Particular the "no backlinks" could drop you way down in the serps, but none of the rest of what you describe sounds good. Whether Google is applying the spam rank modifying algorithm or not... and I believe I've seen them use it... simply the amount of fiddling you describe you're doing would confuse Google a lot. As tedster used to describe it...
It's good to follow the old carpenter's adage here: measure twice, cut once.
In the same discussion, Ted also added...
There is some evidence that frequent changes to title elements can cause problems.
Before you go out and get some immediate backlinks, btw, you might do some reading here about how the wrong kinds of backlinks can hurt you. Those are the kinds that are easiest to get artificially.