For a number of weekly updates (so can't say when this started en-masse... roughly most of 2020 so far? by now it was last seen with current 2.239 weekly) I saw during upgrades that sometimes the JVM just quietly dies after running a new WAR version, e.g. last jenkins.log lines would be:

2020-06-05 12:36:32.701+0000 [id=1]     INFO    hudson.WebAppMain#contextInitialized: Jenkins home directory: /var/lib/jenkins found at: SystemProperties.getProperty("JENKINS_HOME")
2020-06-05 12:36:32.897+0000 [id=1]     INFO    o.e.j.s.handler.ContextHandler#doStart: Started w.@596df867{Jenkins v2.239,/,file:///var/cache/jenkins/war/,AVAILABLE}{/var/cache/jenkins/war}
2020-06-05 12:36:33.078+0000 [id=1]     INFO    o.e.j.server.AbstractConnector#doStart: Started ServerConnector at 376a0d86{HTTP/1 dot 1, (http/1.1)}{0.0.0.0:8080}
2020-06-05 12:36:33.092+0000 [id=1]     INFO    org.eclipse.jetty.server.Server#doStart: Started @5878ms

...and then nothing, and no java in `ps` output; detecting the situation was a problem for some time (like telling packages to update, wandering off because it takes tens of minutes for Jenkins to initialize and have a usable UI... and then find it is dead and not even trying to be booting).

Restarting the service in those cases helps, but it has to be done manually since e.g. RPM packages of Jenkins include an init script but not a real systemd service with child process monitoring (and not all distros/deployments favor systemd at all). Also, restarting is a nasty workaround for the original issue of quiet fail.

We do not often restart without also updating, so I can't say if this situation happens randomly for any start or is linked to updates specifically.