When testing the refresh deployment, the process started off smoothly, but eventually the task sequence restarted the computer. When the computer tried to boot back up, there was no OS on the drive. The only clue as to the cause was found in the bdd.log file:
FAILURE (5456): Unable to determine Destination Disk, Partition, and/or Drive.
The task sequence attempts to back up the original drive to an image before re-installing the OS. Since I had added the format steps under "Refresh Only" (which is above "Backup" in the task sequence), the drive was already wiped before the backup step tried to run. In my case, I don't want a full backup of the computer anyway, so disabling the backup step resolved the issue. If you do want a full backup before the drive is wiped, moving the "backup" step up into or above the "refresh only" group would probably solve this issue.