When loading the article "1" on mobile-html, the app will receive the following message:
https://en.wikipedia.org/api/rest_v1/page/mobile-html/1
Uncaught ReferenceError: pcs is not defined
But, if you try to load "2" on mobile-html, it will work without any issue.
Looks like the "1" page has not been updated/purged, and the source code of https://en.wikipedia.org/api/rest_v1/page/mobile-html/1 does not contain the following stylesheet:
<link rel="stylesheet" href="//meta.wikimedia.org/api/rest_v1/data/css/mobile/pcs">
We may close this ticket since not all pages have been updated/purged.