X-robots-tag
Seems that AMPBench tool complaint if sees x-robots-tag in response:
curl -I https://www.warungtutorial.com/ HTTP/2 200 x-robots-tag: all content-type: text/html; charset=UTF-8 expires: Fri, 08 Feb 2019 03:29:39 GMT date: Fri, 08 Feb 2019 03:29:39 GMT cache-control: private, max-age=0 last-modified: Fri, 08 Feb 2019 03:20:11 GMT etag: W/"94c68ca9d0e1f69560d6da9c8be07953c9846d2fc60e727e8b5a6fd531192532" x-content-type-options: nosniff x-xss-protection: 1; mode=block content-length: 0 server: GSE
message in AMPBench is: "X-Robots-Tag Header FAIL Found header entry for X-Robots-Tagall".
All in this tag mean "index everything" so this isn't should be as error. Values as "none" or "noindex" are the one that should be errors according to specification: https://developers.google.com/search/reference/robots_meta_tag