This bug is reported in launchpad: Elantech touchpad stops working after suspend.

Everytime you wake up from suspending, You have to "unload&load psmouse module manually".

So the solution is create a script.

sudo vim /lib/systemd/system-sleep/trackpoint

with:

#!/bin/sh
case $1/$2 in
  pre/*)
    echo "Going to $2..."
    # Place your pre suspend commands here, or `exit 0` if no pre suspend action required
    modprobe -r psmouse
    ;;
  post/*)
    echo "Waking up from $2..."
    # Place your post suspend (resume) commands here, or `exit 0` if no post suspend action required
    sleep 2
    modprobe psmouse
    ;;
esac

Don't forget grant excute promission.

sudo chmod +x /lib/systemd/system-sleep/trackpoint

Reboot&Enjoy.

Links:
https://askubuntu.com/questions/671910/touchpad-not-working-after-suspending-laptop
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1490130