Ultra 4+ not rebuilding volume prior to expansion

I'm trying to upgrade my Ultra 4+ from 2 x 2TB disks to 2 x 3 TB disks. Running RAIDiator 4.2.20. I started out by replacing one disk (disk 2) with the new 3TB disk. After a minute or two the NAS found the drive & started the RAID sync. Six hours later it was done. This morning I replaced disk 1 with another 3TB disk. The log says the new disk was detected & that the volume will be rebuilt with Disk 1, but 20 minutes later I still do not have the "Raid Sync Started" message in the log. The Health screen still shows a flashing yellow light for Disk 1, and the drive info for disk 1 is still from the 2 TB drive, and the status is "Dead". So, now what... :)