This seems Unbreak now to me, as it seems like about every Page Preview by every reader from everywhere in the world is affected (I can reproduce in Asia). "Switch summary to proxying to the backend service" from https://gerrit.wikimedia.org/r/#/c/mediawiki/services/restbase/deploy/+/519107/ (https://github.com/wikimedia/restbase/commit/dd1bc3b535a91ca0e7513a4460a29d3815969ca0) seems most likely at a glance to be the issue, since only the page summary is not updating.

Dup of T222859?
Probably hit the Catalan Wikipedia first due to the train..

Now every time an edit is made to an article where there are unknown parameters, the preview-only warning is shown on view until the page is purged; see report of issues at VPT.

There's a broken comment in both pages

<!-- Inline citations added to your article will automatically display here. See en.wikipedia.org/wiki/WP:REFB for instructions on how to add citations. --

which should be

<!-- Inline citations added to your article will automatically display here. See en.wikipedia.org/wiki/WP:REFB for instructions on how to add citations. -->

resulting the rest of page to be treated as a comment, including the templates to be substed.

The contrast of links against the background is 3.91, below the 4.5 required by WCAG AA for normal text. (going off this )

.fmbox shouldn't be treated like a page issue because the class is not used for page issues - it is used for edit notices and system messages (see documentation of template here). Treating fmbox as a page issue also breaks things on enwiki e.g on (view logged out)
https://en.m.wikipedia.org/w/index.php?title=Barack_Obama&action=edit&mobileaction=toggle_view_mobile

Indeed already configurable on-wiki through Template:Reviewednote-NPF and Template:Unreviewednonote-NPF (Messages for deletion tags, along with what appears to be every type of message sent, are also configureable, e.g Template:Empty-warn-NPF)