The file 53disable_unattended_upgrades, located in /usr/share/initramfs-tools/scripts/casper-bottom is not executable so presumably it didn't get run and the -security pocket is still enabled in /etc/apt/apt.conf.d/50unattended_upgrades.
The file 53disable_ unattended_ upgrades, located in /usr/share/ initramfs- tools/scripts/ casper- bottom is not executable so presumably it didn't get run and the -security pocket is still enabled in /etc/apt/ apt.conf. d/50unattended_ upgrades.