Try adding this new systemd-hibernate-resume.service service file to your dracut config:
/etc/dracut.conf.d/resume.conf
add_dracutmodules+=" resume "
install_items+=" /usr/lib/systemd/system/systemd-hibernate-resume.service "
Then rebuild the initramfs with sudo dracut-rebuild and test if it makes any difference. 
Source: [systemd 255rc2] hibernation with dracut / [testing] Repo Forum / Arch Linux Forums