Due to some sort of a race (bios, kernel or udev) my root file system yesterday
ended up being called /dev/sdb2 (instead of /dev/sda2 as it normally is). And
then when I ran zypper up to install the latest kernel update the results were
an unbootable system. Conclusion: something somewhere is using the "physical
device name" instead of the drive UUID to locate the root file system.

I do not intend wasting any time trying to recreate this problem since I fixed
my system already and it is apparently caused by a rare random event, but I did
think it might save you some time to have a look at the zypper update stack for
the kernel because I have seen quite a few unexplained unbootable kernel
updates coming out of bugzilla over the years.

Thank you for your time.