Initial hyptothesis was that restbase got an empty page stuck in it, since PCS locally seems to work, but
https://ab.wikipedia.org/wiki/%D4%A4%D1%85%D1%8B%D0%BD%D2%B7%D0%BA%D3%99%D1%8B%D0%BD%D0%BC%D0%B7%D0%B0_17?redirect=false&action=purge didn't seem to fix the problem. Deserves further investigation.

It looked like a restbase problem. I triggered an action=purge and purged the page on edge and response is not empty.

Got similar problem, but with bm.wikipedia.org
Check the output of https://bm.wikipedia.org/api/rest_v1/page/mobile-html/Bamaj%C9%9B
Actual output

{
"type": "https://mediawiki.org/wiki/HyperSwitch/errors/query_error",
"title": "Error in Cassandra table storage backend",
"method": "get",
"uri": "/bm.wikipedia.org/v1/page/mobile-html/Bamaj%C9%9B"
}

Expected
mobile-html representation of the desktop article - https://bm.wikipedia.org/wiki/Bamaj%C9%9B

_

Upd: it is working now.

@vadim-kovalenko Hey! Is this still an issue? It looks like its working now.

@Jgiannelos , yes, it is working now.

Let's close this then, we do not have a repro