Long time openelec pxe user here.
I too have switched to libre and was suffering from this.
I created an account here just to thank you guys and explicitly show the edits for future google searches 
Computer now reboots and shutdown like you would expect (FINALLY!!!)
For the record : here's what I have (for an htpc with onboard lan)
in .../nfsroot/libreELEC_krypton/.config :
connman_main.conf
Code
NetworkInterfaceBlacklist = eth,vmnet,vboxnet,virbr,ifb,docker,veth,ve-,vb-and in .../nfsroot/libreELEC_krypton/.config/system.d
copied
Code
[code]
cp /usr/lib/systemd/system/connman.service .../nfsroot/libreELEC_krypton/.config/system.d
[/code]
edited like this (added my home gateway first (192.168.0.1):
Code
[Unit]
Description=Connection service
DefaultDependencies=false
Conflicts=shutdown.target
Before=network.target multi-user.target shutdown.target
After=dbus.service
Wants=network.target
[Service]
Type=dbus
BusName=net.connman
Restart=on-failure
EnvironmentFile=-/run/libreelec/debug/connman.conf
ExecStartPre=-/bin/sh -c "echo -e 'nameserver 192.168.0.1\nnameserver 8.8.8.8\nnameserver 8.8.4.4' > /etc/resolv.conf"
ExecStartPre=-/bin/sh -c "cat /storage/.cache/hostname > /proc/sys/kernel/hostname"
ExecStartPre=-/bin/sh -c "cat /storage/.config/hosts.conf > /etc/hosts"
ExecStartPre=/sbin/ifconfig lo 127.0.0.1 netmask 255.0.0.0 up
ExecStart=/bin/sh -c ". /usr/lib/connman/connman-setup; exec /usr/sbin/connmand -nr $CONNMAN_MAIN $CONNMAN_DEBUG"
StandardOutput=null
RestartSec=2
StartLimitInterval=0
[Install]
WantedBy=multi-user.target