Can't say for sure but given that CentralNotice doesn't follow the train, it can be caused by mismatch between the code of minerva/core and CN and not being backward compatible.

It looks like this change is the culprit https://github.com/wikimedia/mediawiki-skins-MinervaNeue/commit/7530f1c14571ef1719d22ca6a80883035dce61fd#diff-3b487d87a7042d7284beb9033bd170a3126814e723623f2dc9b7167a627b7b32L682

CentralNotice injects the banners into this element after page load:

$( function () {
	$( '#siteNotice' ).prepend( '<div id="centralNotice"></div>' );
} );

The sites were rolled back for the unrelated T296098 so banners are working again for now.

Adding @cjming and @Jdlrobson who worked on the change above (gerrit link), it definitely looks like the cause.

Change 740213 had a related patch set uploaded (by Clare Ming; author: Clare Ming):

[mediawiki/skins/MinervaNeue@master] Fix banners to show CentralNotice

https://gerrit.wikimedia.org/r/740213

Change 740213 merged by jenkins-bot:

[mediawiki/skins/MinervaNeue@master] Fix banners to show CentralNotice

https://gerrit.wikimedia.org/r/740213

Change 740246 had a related patch set uploaded (by Nray; author: Clare Ming):

[mediawiki/skins/MinervaNeue@wmf/1.38.0-wmf.9] Fix banners to show CentralNotice

https://gerrit.wikimedia.org/r/740246

The train is blocked on this task and another one that is a memory leak of some sort ( T296098 ). To debug that second issue, we need to deploy the code to production for debugging which we can only do once this CentralNotice bug has been backported. It is scheduled at 19:00 UTC (thanks @cjming), I am willing to backport it earlier today but would need a confirmation as to how I can reproduce and confirm the backport work.

@kai.nissen @Pcoombe @AbbanWMDE my understand is that https://en.m.wikipedia.org/?banner=wmua_wikiscience_2021 was not showing the banner (it does now since we have rolled back MediaWiki). On the new MediaWiki we don't see the banner https://m.mediawiki.org/?banner=wmua_wikiscience_2021 since it is running 1.38.0-wmf.9.

If I backport the code and roll it on the mwdebug hosts, I should see the banner on mediawiki.org which would confirm the fix works and this task can thus be resolved?

I am willing to port it during today UTC morning backport window at 12:00 - 13:00 UTC (one hour from now).

@hashar Yes, if you see a banner when adding banner=wmua_wikiscience_2021 (or any banner) to the URL, the task is resolved.

Ignore the above comment ^ I missed an "if"

Thanks! I will deploy the backport config patch during the morning backport window. I will do the patch after the others have been completed.

Change 740246 merged by jenkins-bot:

[mediawiki/skins/MinervaNeue@wmf/1.38.0-wmf.9] Fix banners to show CentralNotice

https://gerrit.wikimedia.org/r/740246

Mentioned in SAL (#wikimedia-operations) [2021-11-22T12:11:25Z] <hashar@deploy1002> Synchronized php-1.38.0-wmf.9/skins/MinervaNeue: Fix banners to show CentralNotice - T296077 (duration: 01m 04s)

Thanks, everybody!