These are the relevant lines from unattended-upgrades-dpkg.log:
Setting up unattended-upgrades (0.90ubuntu0.1) ...
Replacing config file /etc/apt/apt.conf.d/50unattended-upgrades with new version
update-rc.d: warning: start and stop actions are no longer supported; falling back to defaults
These are the relevant lines from unattended- upgrades- dpkg.log:
Setting up unattended-upgrades (0.90ubuntu0.1) ... apt.conf. d/50unattended- upgrades with new version
Replacing config file /etc/apt/
update-rc.d: warning: start and stop actions are no longer supported; falling back to defaults
Notice the middle line.