Debian 10 Buster: computer won't power-off completely (nor suspend/hibernate)

Question

In my new Debian 10 Buster installation, neither suspend nor hibernate work. Poweroff halts shortly before the end and I suspect this is a related issue. I suspect suspend/hiberante won't work until the computer can power off itself

Started Power-Off Reached target Power-Off.

Then: A series of systemd-shutdown messages, and the computer remains stuck in this state. Waiting, even minutes, does not work.

What have I checked so far:

swapon

NAME      TYPE       SIZE USED PRIO
/dev/sda2 partition 15.6G   0B   -2

cat /etc/initramfs-tools/conf.d/resume
RESUME=UUID=857ff79e-586a-4364-9ee7-47c77f6debd1

update-initramfs -u -k all
apt-get install --reinstall initramfs-tools

cat /etc/default/grub | grep RESUME
GRUB_CMDLINE_LINUX="RESUME=UUID=857ff79e-586a-4364-9ee7-47c77f6debd1"

blkid | grep swap
/dev/sda2: LABEL="swap" UUID="857ff79e-586a-4364-9ee7-47c77f6debd1" TYPE="swap" PARTUUID="e0c5913d-02"

It's running the 4.19 kernel. When running the 4.9, poweroff works, and hibernates manages to save the image, but fails to wake up. Running 4.9 also poses additional issues, like not being able to dim the screen, so it would not be an option.