I think it is gone again, but after reading the article you linked it makes sense why it is coming and going. "Users are able to vote on whether the fact-check

I think it is gone again, but after reading the article you linked it makes sense why it is coming and going. "Users are able to vote on whether the fact-checks are helpful or not. They can appear or disappear based on how many people found them to be helpful, Twitter's Vice President of Product Keith Coleman said Friday."