From the command line restoring the most recent backup (I figured out this sed trick today, but it was the same if I copy/pasted).
$(discourse restore |sed -n '3p')
And the backup is on S3 restored from a slightly older version:
Discourse 3.4.0.beta1-dev - https://github.com/discourse/discourse version a3d61ba1c43931eb688f9b2b85c207b5bab02b8c
to
Discourse 3.4.0.beta2-dev - https://github.com/discourse/discourse version f405c021ebd36d5f11499159bd2b54098356a8f9"