Visit https://en.wikipedia.beta.wmflabs.org/wiki/Dog?debug=true and hover over "the first domesticated animal" from the first paragraph. Nothing happens. A generic preview should show up.
Hovering over "working" from the same paragraph show a generic preview.
This only happens when a page is a redirect to another page that doesn't exist. I suppose it's rare in production, but on the beta cluster, we may have more cases like this.
it seems we handle RESTBase 404s differently from mediawiki API.
No change should be necessary in the REST endpoint.
Upon hovering over "the first domesticated animal" https://en.wikipedia.beta.wmflabs.org/wiki/Dog?debug=true I should see a popup similar to: