Jenkins gives a notification that there is a new version (2.149).
Click Upgrade Automatically.
Jenkins starts the download to jenkins.war twice,
and gives twice the blue ball and message 'installed'
There are at this time 3 files on disk: jenkins.war, jenkins.war.bak and jenkins.war.tmp
Set 'restart' checkbox: only .war.bak remains after service is stopped.
Jenkins fails to start because jenkins.war is not found.
third attempt (while writing this report) succeeded.
It only downloaded & installed once after setting 'udgrade automatically'.
There are no other users on this serrver who will start an upgrade.