I configured unattended upgrades based on the official Debian guide found here: https://wiki.debian.org/UnattendedUpgrades.
Interesting configuratin files can be found here: https://mega.nz/#F!ezokiaia!wm1FduLak8-60aXHQZqQtg. Feel free to ask for more information.
[PMS - Upgrade]
Below is the terminal output when I manually test the unattended upgrade (doesn't find the Plex Media Server upgrade). Afterwards I do the apt-get update command (nothing to update) and the apt-get upgrade command (the Plex Media Server upgrade gets installed correctly).
[Google Chrome Stable - Upgrade]
The same counts for the Google Chrome Stable upgrades, they don't get installed during the unattended upgrade, but they do get installed during the apt-get update process.
[Debian - Update]
The same counts for the debian stretch-updates, they don't get installed during the unattended upgrade, but they do get installed during the apt-get update process.
[MEGA - Update]
For MEGA the case is a bit different, since it always installs the same update when performing apt-get update, the issue of that lies somewhere else (although I am also clueless why it behaves like that...).
[Terminal Output]
root@Desktop:/home/maxim# unattended-upgrade -d
Initial blacklisted packages:
Initial whitelisted packages:
Starting unattended upgrades script
Allowed origins are: ['origin=Debian,codename=stretch,label=Debian-Security']
Checking: google-chrome-stable ([<Origin component:'main' archive:'stable' origin:'Google LLC' label:'Google' site:'dl.google.com' isTrusted:True>])
Checking: plexmediaserver ([<Origin component:'main' archive:'public' origin:'Artifactory' label:'Artifactory' site:'downloads.plex.tv' isTrusted:True>])
pkgs that look like they should be upgraded:
Fetched 0 B in 0s (0 B/s)
fetch.run() result: 0
blacklist: []
whitelist: []
No packages found that can be upgraded unattended and no pending auto-removals
root@Desktop:/home/maxim# apt-get update
Get:1 http://security.debian.org/debian-security stretch/updates InRelease [94.3 kB]
Hit:2 http://ppa.launchpad.net/graphics-drivers/ppa/ubuntu eoan InRelease
Ign:3 http://dl.google.com/linux/chrome/deb stable InRelease
Hit:4 http://linux.teamviewer.com/deb stable InRelease
Hit:5 http://files.eid.belgium.be/debian stretch InRelease
Hit:6 http://files2.eid.belgium.be/debian stretch InRelease
Hit:7 http://dl.google.com/linux/chrome/deb stable Release
Ign:8 https://downloads.plex.tv/repo/deb public InRelease
Hit:9 https://downloads.plex.tv/repo/deb public Release
Ign:10 http://ftp.be.debian.org/debian stretch InRelease
Get:11 http://ftp.be.debian.org/debian stretch-updates InRelease [91.0 kB]
Hit:12 http://ftp.be.debian.org/debian stretch Release
Hit:13 https://updates.signal.org/desktop/apt xenial InRelease
Get:17 https://mega.nz/linux/MEGAsync/Debian_9.0 ./ InRelease [1,306 B]
Fetched 187 kB in 1s (103 kB/s)
Reading package lists... Done
root@Desktop:/home/maxim# apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages will be upgraded:
google-chrome-stable plexmediaserver
2 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B/150 MB of archives.
After this operation, 73.5 MB of additional disk space will be used.
Do you want to continue? [Y/n] y
Reading changelogs... Done
(Reading database ... 172450 files and directories currently installed.)
Preparing to unpack .../google-chrome-stable_78.0.3904.87-1_amd64.deb ...
Unpacking google-chrome-stable (78.0.3904.87-1) over (78.0.3904.70-1) ...
Preparing to unpack .../plexmediaserver_1.18.1.1973-0f4abfbcc_amd64.deb ...
Removed /etc/systemd/system/multi-user.target.wants/plexmediaserver.service.
Unpacking plexmediaserver (1.18.1.1973-0f4abfbcc) over (1.18.0.1944-f2cae8d6b) ...
Processing triggers for mime-support (3.60) ...
Processing triggers for desktop-file-utils (0.23-1) ...
Processing triggers for menu (2.1.47+b1) ...
Processing triggers for libc-bin (2.24-11+deb9u4) ...
Processing triggers for man-db (2.7.6.1-2) ...
Processing triggers for gnome-menus (3.13.3-9) ...
Setting up google-chrome-stable (78.0.3904.87-1) ...
Setting up plexmediaserver (1.18.1.1973-0f4abfbcc) ...
Created symlink /etc/systemd/system/multi-user.target.wants/plexmediaserver.service → /lib/systemd/system/plexmediaserver.service.
Processing triggers for menu (2.1.47+b1) ...
Processing triggers for libc-bin (2.24-11+deb9u4) ...
root@Desktop:/home/maxim#