So yeah, this looks exactly like a more frequent bug 1421009, which was due to a dbus mutex hang.
Here are some possibly related dbus hang bugs:
Bug 1421009 (vivid, basically same bug as this one) Bug 1417773 (RTM) Bug 1421308 (vivid?)
The most reliable reproducer of the bunch is bug 1421009, which involves reflashing a bunch.
And it also suggests the earliest sign of the bug as vivid image 106.
So yeah, this looks exactly like a more frequent bug 1421009, which was due to a dbus mutex hang.
Here are some possibly related dbus hang bugs:
Bug 1421009 (vivid, basically same bug as this one)
Bug 1417773 (RTM)
Bug 1421308 (vivid?)
The most reliable reproducer of the bunch is bug 1421009, which involves reflashing a bunch.
And it also suggests the earliest sign of the bug as vivid image 106.