At boot time, the following message can pop up :
WARNING : Failed to connect to lvmetad. Falling back to device scanning
This message is displayed, whether running Debian stable or Debian testing.
To get rid of this message, disable lvmetad in /etc/lvm/lvm.conf
Update the initramfs for the current kernel your system uses :
update-initramfs -k $(uname -r) -u; sync
Reboot your system and you’re done !
This issue has already been reported in the Debian bug tracking system : #846946