It's very sporadic, somewhat rare, so I won't really open a thread on the forums themselves, but I'll just collect links and snippets here hoping there's some way to fix it, if it doesn't get fixed "by itself"/by systemd/debian developers first.
Quote:
I have Mate desktop and Slim installed:
halt_cmd /sbin/systemctl poweroff -i
reboot_cmd /sbin/systemctl reboot -i
like this, when I request shutdown all applications exit and then slim restart
...