debian9 amd64 failure to connect to lvmetad, falling back to device scanning

Hello:
On a vintage VAIO I have no problems with amd64 stretch. With a raid1-based
on the X79 chip, upgrading from jessie to stretch (I need a higher CUDA
version than available on jessie for latest experimental NAMD molecular
dynamics) went on regularly. However, the command

# systemctl set-default multi-user.target

(which worked fine on said VAIO to boot at the $ linux prompt) led to
failure to connect to lvmetad, falling back to device scanning, whereby an
endless disk scanning begun.

I tried:

1) Super grub2 disk: OK it led to clean boot but I found no way to fix the
problem.

2) Accessing the X79 computer from said VAIO (both are on a LAN) equally
allowed to manage everything but I was unable to fix the problem.

3) From said VAIO:
 # systemctl enable lvm2-lvmetad.service

OK, but it was lost on needed reboot.

I never had to reinstall a debian amd64 but this time I am lost.

Thanks for any kind suggestion

francesco pietra