All known issues are posted in the Announcement wiki with a workaround
Is important that after the update you either shutdown the system or you reboot. If you didn’t do that and let it run, it might have gotten in sleep mode and the waking up didn’t work … etc etc.
You mean the drivers for your GTX 550 ? Or is a typo about the drivers version you installed ? 455xx are the latest, so maybe you wanted to write 450xx ?
make sure you run from TTY:
sudo pacman-mirrors -f && sudo pacman -Syyuu
sudo mhwd -i pci video-nvidia-450xx
or
sudo mhwd -i pci video-nvidia-455xx
depending what you want and if your GPU is supported.