Hi David,
FYI, UPD worked Nov 21, as noted prior, it reported the same error and "Not finished" on Nov 22 and completed Nov 23. All were with WP Better Security activated, which I couldn't deactivate in time for the backup.
The successful Nov 23 backup log shows a warning that may have something to do with it:
Your website is visited infrequently and UpdraftPlus is not getting the resources it hoped for; please read this page: http://updraftplus.com/faqs/why-am-i-getting-warnings-about-my-site-not-having-enough-visitors/
We're currently using shared hosting and sometimes it's slow serving pages. We'll likely move to cloud hosting in next few weeks so will know then if this was the problem.
In the meantime, we'll continue monitoring and manual updating when we have to.
Thanks.