I’ve installed Debian buster (testing at the time of writing) on a new Dell Latitude 5580 laptop, and one annoyance I’ve found is that the laptop would almost always resume as soon as it was suspended.
AFAIU, it seems the culprit is the network card (Ethernet controller: Intel Corporation Ethernet Connection (4) I219-LM) which would be configured with Wake-On-Lan (wol) set to the “magic packet” mode (ethtool enp0s31f6 | grep Wake-on would return ‘g’). One hint is that grep enabled /proc/acpi/wakeup returns GLAN.
There are many ways to change that for the rest of the session with a command like ethtool -s enp0s31f6 wol d.
But I had a hard time figuring out if there was a preferred way to make this persistant among the many hits in so many tutorials and forum posts.
My best hit so far is to add the a file named /etc/systemd/network/50-eth0.link containing :
[Match] Driver=e1000e [Link] WakeOnLan=off
The driver can be found by checking udev settings as reported by udevadm info -a /sys/class/net/enp0s31f6
There are other ways to do that with systemd, but so far it seems to be working for me. Hth,