The server was rebooted. The lock files exist in a tmpfs in memory
temporary directory which evaporates at shutdown and must be created
new at boot time. For reasons not yet explained the boot time
creation did not happen this boot. It usually happens. We reboot
servers as required for security upgrade kernels and other reasons.
But for some reason it did not run this time.
It's now on my task list to figure out why and to ensure that whatever
is currently broken is fixed so that future reboots will work
correctly and won't have this problem.