This symptom seems to have more than one root cause. For me, I had more than one entry in /etc/crypttab, one being completely wrong. It was probably a left-over from me switching hard drives a while ago, but then the symptom only started to appear after a 14.04 -> 16.04 upgrade.
Just in case it helps someone:
This symptom seems to have more than one root cause. For me, I had more than one entry in /etc/crypttab, one being completely wrong. It was probably a left-over from me switching hard drives a while ago, but then the symptom only started to appear after a 14.04 -> 16.04 upgrade.