I have two boards, and both are fully assembled so I can't test the bare PCB. They both behave the same way so I'd say it's unlikely to be faulty parts unless it was a batch of faulty parts.
I tried running the power for around 30 seconds to see what gets hot, and no sign of black traces and I don't feel anything getting hot other than the 1N5400 diode that sits in between the incoming 12v and the DC-DC converter. The DC-DC supply and TVS diode both don't get warm at all. Does this help point any fingers??
The components all appear to be the correct way around and as per the previously working Rev 3 board...
EDIT: I tried powering the board up via 5v directly on the DC-DC converter output to cut out the 12v part of the PCB and the same problem occurs, though the TVS diode now gets hot... Trying to work out what that means??