maybe it would be a good idea to switch to unattended-upgrades?
I have never managed to get it to work :( I have set it up on several machines and nothing ever got upgraded whatever the config I set. After spending too much time trying to get it to work I decided to use my own script
we added documentation for unattended-upgrades to the tor relay guide, I hope this is helpful for you:
https://trac.torproject.org/projects/tor/wiki/TorRelayGuide/DebianUbuntuUpda...
maybe give it a try and let us know if it doesn't work for you?