Before deploying, it was noted that wtp2019.codfw.wmnet was down, but since that's in the backup cluster, it seemed fine to proceed. However, mistakenly, the target was not removed before attempting the deploy.
The canaries deployed cleanly but the fetching stage failed for the first group, since the above node was part of it. When asked to rollback, the rollback failed for the same reason and the deploy exited with the canaries still on the new commit.
See the paste P4029 for the logs.
Maybe scap should verify all the targets are up before attempting the deploy?