I've been getting instances during the last 4/5 days where G has been labelling some of my KW 'At Risk'
Nothing unusual about that, except that these KW have been showing a CTR of 2% plus over the last two weeks.
I've sent G emails pointing this out, and although I have yet to hear from them, my KW are still functioning.
I suspect a malfunction in their sytem, but as I'm still getting impressions and Clicks on these KWs, I'm not too concerned.
All I can suggest is to send G an email.
As for CTR - its Google's site only that matters for 'at risk' - not partner or content searches:
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