[Libguestfs] firstboot randomly can't find script

[Charles]

I am running the stock libguestfs on latest Ubuntu 16.04 (1:1.32.2-4ubuntu2).

My guests are also Ubuntu 16.04.

I am running virt-sysprep with --firstboot-command 'dpkg-reconfigure
openssh-server'.

This works 90% of the time, but occasionally when a new guest first
starts it can't find the script:

~# cat virt-sysprep-firstboot.log
/etc/init.d/virt-sysprep-firstboot start
Scripts dir: /usr/lib/virt-sysprep/scripts
=== Running /usr/lib/virt-sysprep/scripts/0001-dpkg-reconfigure-openssh-server
===
/usr/lib/virt-sysprep/firstboot.sh start
Scripts dir: /usr/lib/virt-sysprep/scripts
/etc/init.d/virt-sysprep-firstboot: 35:
/etc/init.d/virt-sysprep-firstboot:
/usr/lib/virt-sysprep/scripts-done/0001-dpkg-reconfigure-openssh-server:
not found

As such, I cannot ssh into these guests without opening them manually
on the host and running the dpkg reconfigure command.

This bug seems similar, but I cannot find other reports or fixes:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=773106

Any suggestions to debug or workaround?