Thanks for the pointer. I think its clear that I am not an expert on this job... However, I note that both the original failed run and another log this:
Warning: Permanently added '200.225.47.19' (ED25519) to the list of known hosts.
rsync: [sender] link_stat "/var/lib/zuul/builds/12aacd4951a64c0abef5cfe1bf925c2e/work/ca-bundle.pem" failed: No such file or directory (2)
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1338) [sender=3.2.7]
Which seems like it might be causing the compute node to not start? I certainly cannot see any logs from nova on the compute node's zuul output.
I'll continue to dig.
Michael