Steps to reproduce:
1. Raspberry pi installation with SD-card.
https://archlinuxarm.org/platforms/armv6/raspberry-pi
2. Update:
> pacman -Syu
3. Reboot
I've done this with two Rasbperry pis with different SD cards and each time the raspberry pi will not come back on the network. It doesn't respond to pings.
Someone on Reddit's reported the same thing, but managed to get it working by leaving it 30 minutes and attaching a screen. That's not worked for me, and the screen shows only white fuzz - no tty visible through the HDMI attachment.
Both Pis have been working fine headless for some months and were based on the above instructions.