Thanks for the responses. I didn't add a LABEL to the btrfs partitions, Leap 15.4 installation did. I think this does tell me what's going on. I didn't keep notes on everything I tried but I think that when I first plugged in the disk, there was a mount problem. I used a mount command to try to...
I recently installed openSUSE Leap 15.4 and it created a VFAT partition for boot, btrfs partition for my data and a swap partition. The directory /home has all my data as expected.
The /etc/fstab entry for /home looks like this:
LABEL=M15-HOME /home btrfs subvol=/@/home...