Like the title sez... banners are not working on the several mobile sites.
This can be seen by opening the network tab in the browser developer tools and going to the banner preview link next to each host name, below.
For the first two sites, there are two requests to Special:BannerLoader: first to m.wikimedia.org, which redirects to www.wikimedia.org, which returns a 404. On Wikisource, we get a request to BannerLoader on the unresolvable m.meta.wikimedia.
The cause of the bug is our misuse of the function MobileContext::getMobileUrl() in CentralNotice.hooks.php. That function is designed to work only for the URL of the current wiki. However, we always call it to try to get the mobile URL of meta.wikimedia.org. getMobileUrl() works by applying a template defined by $wgMobileUrlTemplate. The value of this variable is different for the sites in question (see [[ https://github.com/wikimedia/operations-mediawiki-config/blob/8dcf0de952c988557272ff1726c37cea90010169/wmf-config/InitialiseSettings.php#L14748-L14754 | InitialiseSettings.php ]]).
tl;dr: config + incorrect use of a function, but no obvious solution...
Maybe the cleanest route will be to reform how $wgCentralSelectedBannerDispatcher works...
Also note that the client-side JS is not handling the incorrect banner loader calls as expected. (I'll file a separate bug for that...)