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.