Sometimes Google may remove a featured snippet from showing in the search results because it doesn't comply with its own internal policies or guidelines. Google currently does not notify webmasters when such a removal happens but Danny Sullivan from Google said the company is considering doing so.

Danny Sullivan said on Twitter "We don't [notify webmasters of featured snippet removals] as it's not a manual action against the page itself." "It is something we're considering, though," he added. He also said "There may be other ways to show eligibility for particular features."

Here are the tweets so you can see the context:

#askgooglewebmasters does Google review all featured snippet removal requests before removing from the SERP? How long does this process typically take? Are there penalties for sites that have had snippets marked for removal? Do you notify these sites?

Thanks! pic.twitter.com/cnGq9dO3ZR — Brian Freiesleben (@type_SEO) August 6, 2019

We don't as it's not a manual action against the page itself. It is something we're considering, though. There may be other ways to show eligiblity for particular features. — Danny Sullivan (@dannysullivan) August 14, 2019

Google's internal policies say they do remove featured snippets manually. Here is what Google says:

We also manually remove any reported featured snippets found to be in violation of our policies, so as to provide fast protection in the sensitive areas these cover. If this review process discovers a web site has other featured snippets that are routinely against our policies -- or the site itself violates our webmaster guidelines -- the site may no longer be eligible for featured snippets. We do not manually remove featured snippets reported for issues that do not violate our policies. These are dealt with by studying the issues in more depth, then improving our automated systems to do a better job in the future.

I think a notification would be nice to have, so at least you can take steps to do better and regain the featured snippet?

Forum discussion at Twitter.