One of the new Google snippet controls, the new meta tags, recently launched, had a bug where it can trigger Google to deindex the specific page. If you used max-image-preview tag and set the value to none, it would result in Google removing the page from the index. Google confirmed the issue and said a fix is rolling out and the affected pages will be reprocessed....
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New Google Meta Tag Resulted In Pages Not Being Indexed: Now Fixed
seroundtable.com