I can confirm the mentioned warnings about LVM volume groups on all my
Debian Stretch systems. Messages seems to be caused by the running order
of initramfs scripts in "/usr/share/initramfs-tools/scripts/local-*" -
"lvm2" script seems to be run before "cryptroot" script. This is caused
by lines 10 to 16 in
"/usr/share/initramfs-tools/scripts/local-*/cryptroot" - when scripts
run in a default alphabetic order ("cryptroot" then "lvm2") no warnings
seems appear.
Note that I made more modifications to my "lvm2" and especially
"cryptroot" initramfs scripts, so if somebody can confirm that just
changing the run order of default scripts is enough to avoid the
warnings about LVM volume groups it would be nice. Also note the
modified initramfs scripts should be in
"/etc/initramfs-tools/scripts/local-*" and you need to rebuild your
initramfs to test the changes.
When this is confirmed maybe the package for bugs 794971 and 544651
should be changed to "cryptsetup" instead of "lvm2"?
Regards
Bakhelit