I've been poking around looking at this but cant see anything that jumps out, from your side of things anyway.

It could be a fluctuation on Google that you would probably just have to sit out, unfortunately. A lot of people are complaining about massive fluctuations/drops from 4th June onwards. You can read more here.

Are you seeing any other keywords drop?

Those addresses you see are internal networks although the 158.XXX address belongs to a US company. By any chance are you seeing cgi-bin/afterWorkOptions.cgi on those referrals? Its a safe browsing filter.

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