Wild Fluctuations in SERPs for Months On End

I experienced this same situation maybe a year ago, and tried a post here to see if anyone else had experienced it. As I recall I didn't get any answer. The situation resolved itself after about a month without me doing anything special. Same situation now, but it has been going on for at least 6 months.

A website where I'm tracking several keywords. All of them jump around the SERPs wildly, almost on a daily basis. From a high of about 30 to a low of about 250. Over and over and over in a big cycle, like this:



SEO I've done on this site is the same as the dozens of other sites I work on - most links are from my own VERY private network. All links are in same niche articles, anchor text is a mix of naked urls (www. domainname. com), brand name, and a number of variations of the keywords the client is interested in. Lots of LSI in articles.

Nothing crazy done as far as SEO. No negative SEO attacks on the site. Spent time looking on-site for things like on-site duplicate content, etc. Nothing unusual. I'm okay with SERPs jumping around somewhat, especially as a site rises from no rankings on up to the first page. But this is different, as the keywords constantly jump from #25/#30 to #200/#270 or so.

It's aggravating because I do SEO for well over a dozen other sites for this same person, and every other site is fine. Each site is set up roughly the same (they're all WordPress ecommerce sites). And every site I've done approximately the same SEO type of work. I assume it's algorithmic - there's something on the site that Google's algorithm just doesn't like. But I have no idea what the "doesn't like" part is.

Anyone ever experience something like this? Not just the fluctuations of a new site, but wild up and down rankings on an almost daily basis, for months on end?