Unable to update plugins

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1

Since a few months I am having issues updating installed plugins in my Jenkins. The failure details are as follows:

java.net.SocketTimeoutException: Connect timed out
	at java.base/sun.nio.ch.NioSocketImpl.timedFinishConnect(NioSocketImpl.java:546)
	at java.base/sun.nio.ch.NioSocketImpl.connect(NioSocketImpl.java:592)
	at java.base/java.net.SocksSocketImpl.connect(SocksSocketImpl.java:327)
	at java.base/java.net.Socket.connect(Socket.java:751)
	at java.base/sun.security.ssl.SSLSocketImpl.connect(SSLSocketImpl.java:304)
	at java.base/sun.net.NetworkClient.doConnect(NetworkClient.java:178)
	at java.base/sun.net.www.http.HttpClient.openServer(HttpClient.java:531)
	at java.base/sun.net.www.http.HttpClient.openServer(HttpClient.java:636)
	at java.base/sun.net.www.protocol.https.HttpsClient.<init>(HttpsClient.java:264)
	at java.base/sun.net.www.protocol.https.HttpsClient.New(HttpsClient.java:377)
	at java.base/sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.getNewHttpClient(AbstractDelegateHttpsURLConnection.java:193)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1252)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1138)
	at java.base/sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:179)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.followRedirect0(HttpURLConnection.java:2924)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.followRedirect(HttpURLConnection.java:2833)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1944)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1614)
	at java.base/sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:223)
	at hudson.model.UpdateCenter$UpdateCenterConfiguration.download(UpdateCenter.java:1365)
Caused: java.io.IOException: Failed to load https://updates.jenkins.io/download/plugins/analysis-model-api/13.8.0-902.v26f80296f743/analysis-model-api.hpi to /home/jenkins/plugins/analysis-model-api.jpi.tmp
	at hudson.model.UpdateCenter$UpdateCenterConfiguration.download(UpdateCenter.java:1380)
Caused: java.io.IOException: Failed to download from https://updates.jenkins.io/download/plugins/analysis-model-api/13.8.0-902.v26f80296f743/analysis-model-api.hpi → https://ftp.halifax.rwth-aachen.de/jenkins/plugins/analysis-model-api/13.8.0-902.v26f80296f743/analysis-model-api.hpi
	at hudson.model.UpdateCenter$UpdateCenterConfiguration.download(UpdateCenter.java:1407)
	at hudson.model.UpdateCenter$DownloadJob._run(UpdateCenter.java:2059)
	at hudson.model.UpdateCenter$InstallationJob._run(UpdateCenter.java:2387)
	at hudson.model.UpdateCenter$DownloadJob.run(UpdateCenter.java:2033)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:572)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317)
	at hudson.remoting.AtmostOneThreadExecutor$Worker.run(AtmostOneThreadExecutor.java:121)
	at java.base/java.lang.Thread.run(Thread.java:1583)

This is just one example, but the same details appear for all the plugins I want to update (except of course for the URL that needs to be downloaded)

Jenkins setup:

Jenkins version 2.528.1

2

In the end it turned out that for some reason the proxy setting in Jenkins was gone. When I re-added the Proxy configuration, I could update the plugins.