Good info here about the tiny trunk harness wires and that they are easy to break! I have to pass two decently large cables through that boot right after I get the car, so I’ll pay extra attention to not stressing the OEM wires.Given the kit has no interaction with the cameras at all I would imagine one of the wires that is in the loom that goes up into the trunk has been severed. It’s a tight fit in there to pull the wires for the kit up, and the existing wires that are there are very thin (24awg).
That being said if even recent sentry/dashcam doesn’t show it then it would suggest it’s been broken for a while? Recordings don’t need the cameras to be present to work, of course.
Sorry to say that this sounds like an installation fail