What is happening
Google Ads' Ad Preview and Diagnosis tool has been serving a reCAPTCHA "unusual traffic" screen in place of results for roughly a week. Search Engine Roundtable reports no fix timeline from Google.
The irony is worth naming only because it is also the risk. Ad Preview exists precisely so advertisers do not have to run live searches to see their own ads, and the tool itself is now being treated as unusual traffic.
What to do about it
Read serving status from the campaign instead of the preview
A keyword that is serving accumulates impressions, and one that is not carries a status telling you whether it is low search volume, below the first-page bid, disapproved, or paused. Between impression volume and the status column you can answer "is my ad running" without generating a single search of your own. If the question is geographic or device-specific, segment the same report rather than reaching for the preview.