Update-Manager is calling 'do-release-upgrade' (i.e. ubuntu-release-upgrader) to do the actual upgrade (and print its output), so this is a duplicate of the other bug #1871801 you reported.
Update-Manager is calling 'do-release- upgrade' (i.e. ubuntu- release- upgrader) to do the actual upgrade (and print its output), so this is a duplicate of the other bug #1871801 you reported.