As I suspected, this problem disappeared after manually disconnecting the drives that comprise my BTRFS RAID10 array. Ubiquity and the partitioning tool have had problems with complicated setups over the years from dm-raid to apparently btrfs drives or arrays.
As I suspected, this problem disappeared after manually disconnecting the drives that comprise my BTRFS RAID10 array. Ubiquity and the partitioning tool have had problems with complicated setups over the years from dm-raid to apparently btrfs drives or arrays.