So John Mueller from Google asked on Twitter for specific examples and then when he got some, he replied to them.
@sqimul Would love to hear details, the ones I checked had nothing crazy, zombie-like. Broad threads don't help, I need URLs, queries, etc.— John Mueller (@JohnMu) June 19, 2016
He said in the case that was given to him it was an issue of geotargeting and not having enough quality results in that language. Here are his tweets:
@sqimul This is more about weird geotargeting; it can happen & it's good to get reports like this. Thanks!— John Mueller (@JohnMu) June 19, 2016
@sqimul Looking more, I think the main problem is we don't have a lot of good content for that query in English, so we expand it.— John Mueller (@JohnMu) June 19, 2016
Now of course, that is just based on one example, which I cannot honestly find here, given by one user. You should all try to send examples of this Zombie traffic to John so he can investigate these reports and give us a rock solid answer, if possible.
This Zombie traffic phenomenon is probably not just frustrating to you but also to Google where they have no real details on what the webmaster community is seeing.
Forum discussion at Twitter.