I installed the RPi 2 image on RPi 3 (as recommended by the webpage). Fairly simple, do fdisk, bsdtar, copy boot out to the boot partition. It boots up fine.
None of my changes stick past a shutdown/reboot. Installing packages or editing fstab.
So I'd do (for example) pacman -Syu, and everything would download and install. Or I can pacman -S sudo and set it up, it works, so it is installing at some point.
However after a systemctl reboot (or poweroff) it doesn't work anymore.
Perhaps related, after every reboot or poweroff ssh warns me that 'REMOTE HOST IDENTIFICATION HAS CHANGED'.
Also, I tried running 'sync' just before reboot/poweroff, as well as leaving it for a while (thinking that the systemd SD card saving tricks mentioned here[1] may be to blame). No change.
Could it be:-
1. Power supply problems?
2. Bad micro-SD card?
3. Something else?
[1] - viewtopic.php?f=9&t=10068