When the install was in progress on the good/at the point of failure on the bad I did:
control-f2 to activate another terminal chroot /target apt apt-cdrom
good 20180130: apt 1.6~alpha 7 (amd64) bad 20180216 : apt 1.6~alpha 5 (amd64)
So yes, the version of apt/apt-cdrom is different.
When the install was in progress on the good/at the point of failure on the bad I did:
control-f2 to activate another terminal
chroot /target
apt
apt-cdrom
good 20180130: apt 1.6~alpha 7 (amd64)
bad 20180216 : apt 1.6~alpha 5 (amd64)
So yes, the version of apt/apt-cdrom is different.