During startup of an upgraded environment in an air-gapped network where system property 'hudson.model.UpdateCenter.never' is set to 'true' we see in the log:

Jul 29, 2021 10:13:06 AM WARNING hudson.model.UpdateCenter updateAllSitesNow
Failed to update the update site 'default'. Plugin upgrades may fail.
java.net.UnknownHostException: updates.jenkins-ci.org
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:607)
at sun.net.NetworkClient.doConnect(NetworkClient.java:175)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:463)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:558)
at sun.net.www.http.HttpClient.<init>(HttpClient.java:242)
at sun.net.www.http.HttpClient.New(HttpClient.java:339)
at sun.net.www.http.HttpClient.New(HttpClient.java:357)
at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:1226)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1162)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1056)
at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:990)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1570)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1498)
at hudson.model.DownloadService.loadJSON(DownloadService.java:116)
at hudson.model.UpdateSite.updateDirectlyNow(UpdateSite.java:217)
at hudson.model.UpdateSite.updateDirectlyNow(UpdateSite.java:212)
at hudson.model.UpdateCenter.updateAllSitesNow(UpdateCenter.java:2597)
at jenkins.security.ImpersonatingScheduledExecutorService$1.run(ImpersonatingScheduledExecutorService.java:67)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)

We don't see this in our v2.263.4 instance, so something has changed after that.

Expected behavior is that system property 'hudson.model.UpdateCenter.never' is honored and no check should be done.