Christopher, I do thank you for responding and offering to help, but instead of drilling down to discover the root cause, I've decided to go ahead and just rearrange things to avoid the problem in the future. I'm going to purchase another 10TB drive to replace the 4TB. I'll put the two 12TB drives in one enclosure, and the two 10TBs in the other. That way Scanner won't have the opportunity to get the sizes mixed up. I'll probably end up restoring 20 or 30 TBs of data from backup, but hey that's what backups are for.
Thanks again. And for the record I'm still happy with the Stablebit soft