After installing Leap 42.3 I ran "zypper up" and got the following updates
(there are a few others, but aren't relevant):

The following 10 packages are going to be upgraded:
  dracut                   044-21.7 -> 044.1-23.2
  libsystemd0              228-27.2 -> 228-29.1
  libsystemd0-32bit        228-27.2 -> 228-29.1
  libudev1                 228-27.2 -> 228-29.1
  systemd                  228-27.2 -> 228-29.1
  systemd-32bit            228-27.2 -> 228-29.1
  systemd-bash-completion  228-27.2 -> 228-29.1
  systemd-logger           228-27.2 -> 228-29.1
  systemd-sysvinit         228-27.2 -> 228-29.1
  udev                     228-27.2 -> 228-29.1

There's something in there that causes the next boot to fail due to
dracut-initqueue not being able to find /dev/mapper/system-root. Looking at
/dev/mapper the only file in there is 'control'. 
Running "lvm_scan" causes the volumes to be found and /sys-root to be mounted.

The install is on a single 4TB SATA disk with 3 LVM volumes: system-root
(Btrfs), system-swap and system-home (xfs).