robots.txt stops search engines reading the page

A Disallow rule in robots.txt stops crawlers fetching the page, so they never see its title, text or tags. The address can still show up in results, as a bare link with "No information is available for this page", which is worse than not appearing. It also hides any noindex on the page, because a crawler that can't fetch the page can't read it.

Source: Introduction to robots.txt. We test the rules for Googlebot, falling back to *, the way Google documents matching.

Open /robots.txt and remove or narrow the rule we matched. A leftover from staging is the usual cause:

User-agent: *
Disallow: /

To let everything be crawled, leave Disallow: empty. To keep a page out of search results, don't use robots.txt: allow it to be crawled and give it a noindex meta tag instead.