Steps to replicate the issue (include links if applicable):

• Go to https://test.wikipedia.org/api/rest_v1/page/summary/Maria_Louisa_Bustill

What happens?:

{
    "type": "https://mediawiki.org/wiki/HyperSwitch/errors/not_found",
    "title": "Not found.",
    "method": "get",
    "detail": "404: https://mediawiki.org/wiki/HyperSwitch/errors/not_found",
    "uri": "/test.wikipedia.org/v1/page/html/Maria_Louisa_Bustill"
}

What should have happened instead?:

An API response should appear, including the page summary about the Maria Louisa Bustill page. See https://cs.wikipedia.org/api/rest_v1/page/summary/Praha as a working example.

Other information (browser name/version, screenshots, etc.):

This is the direct cause of T350212.