I had the exact same problem and it was caused by missing modules  and 
drivers in dracut created initramfs that boots the kernel. Try booting to 
livecd or older kernel and run "lsinitrd 
/boot/initramfs-your-failing-kernel-version | less"  and it should list 
included modules.

Open /etc/dracut.conf and modify to include needed ones, in my case sata 
driver was missing and crypt module

add_drivers+="ahci"
add_dracutmodules+="crypt caps"

next run sudo dracut -f /boot/initramfs-your-failing-kernel-version 
your-failing-kernel-version

reboot and hopefully it works. If it still doesn't work you can try 
mkinitcpio.

maanantai 13. heinäkuuta 2015 17.41.50 UTC+3 oliver kirjoitti:
>
> Further to this, I was able to re-create the problem every time using the 
> 6/15 MUSL ISO.  As soon as the kernel is upgraded, the box fails to boot 
> (tried 4.0.x and 4.1.x)
>
> Installing from the 7/13 ISO (with kernel 4.1.2) worked so I think 
> whatever the problem was is now resolved.
>