Comment 159 for bug 1252121

It is still happening in Xubuntu 14.10. After coming back from suspend (closed the laptop lid), NetworkManager is asleep:

RUNNING STATE WIFI-HARDWARE WIFI WWAN-HARDWARE WWAN
running asleep enabled enabled enabled disabled

This workaround works for me: created script /etc/pm/sleep.d/49network-manager:

#!/bin/sh
#
# work around a NetworkManager bug, waking it up after resume (sometimes it
# stays sleeping after resume)
#

case "$1" in
    suspend|hibernate)
 ;;

    resume|thaw)
 nmcli nm status
 nmcli dev status
 state=`nmcli -t -f STATE nm status`
 if [ "$state" = "asleep" ]; then
     echo "waking up NetworkManager"
     nmcli nm sleep false
     nmcli nm status
 fi
 ;;
esac

exit 0

I had removed it to test whether the problem had gone away, but put it back when confirmed it hadn't been solved yet.