This filter appeared a while ago, and the exact number can vary, but if it shows 4 pages, it’s a classic case.
What does this filter indicate?
Your content quality is so low that Google is dropping it from the index.
You need to change your content creation method, because it won’t work in its current form.
In this example, the content was generated from PAA.
Another sign is that pages are also disappearing from the index in Google Search Console. And the classic symptom: impressions are present and then suddenly drop to zero. They might hover for a week, and then it’s over.