So do we have any ideas yet?
I have another site that is acting strange to say the least. If anyone recalls a bit of chatter about an update at the beginning of February this site tanked, lost all SERPS for just about everything, couldn't be found for anything of note at all. At the time I expected it to quickly come back as it was an error but nothing returned. What was annoying, and strange, was it could be still found in other google geos, so for example '**** **** uk' is the main keyword and went from about page 3 in google UK to completely nowhere, but for the same phrase is Google Ireland and Canada (just 2 examples I checked, it carried on ranking around page 3 for months.
The site was pretty gone so many of the links I started changing to another site but did nothing. For the KW I mentioned sometimes the site was about on page 11 but that was it, all the other ones nowhere. Suddenly as the May core update rolled out shot back to page 5 for that and 7 for 'UK **** ****' and 9ish for '**** ****', nothing great but a start. It stuck like that for a couple of weeks with the usually little moves then bombed again, I think it must have been the start of June. Yesterday I noted it had came back for those KW's on page 5 and 7, what happens next is anyone's guess.
Like the other site I have been mentioning in this thread the big swings don't make sense apart from the sites must be triggering a filter that is either pushing the site down or total ignoring some ranking factor, what and why though I am non the wiser. I posted this on google webmaster forums as well for some more info https://support.google.com/webmasters/thread/55524585?hl=en