Comment # 2 on bug 966255 from Robert Schweikert

Appears to be. Fabian Vogt reports a similar issue on the factory ML (Thread:
TW has fallen and cannot get back up) that started around the time of the
inclusion of the 4.4 kernel.

The work around is to add plymouth.enable=0 to the kernel command line.

Having done so I can now also confirm that my initial suspicion of it being
related to the request for the passphrase is correct. After disabling plymouth
the passphrase is requested right after the message " Ignoring BGRT: Invalid
version 0 (expected 1)"