I'm surprised they didn't mention that the only possible culprit is the sensors themselves.
Works like this: there's a pressure sensor before and after the filter matrix. If the flow through the matrix is good, the pressure on the far side will be very slightly less than the pressure before it (because the matrix itself reduces the volume in the pipe, it causes a small pressure increase because it's a restriction in the pipe). If the pressure variation rises beyond a certain point it means that the restriction is too large for good exhaust flow and a regen is required. The car tries to perform one and if unsuccessful, lights the DPF light and tries again. Too many failed attempts and the car goes into limp mode and requires the forced regen.
So the only thing telling the ECU that the DPF is blocking up is the return signal from those two sensors. If the electrical connections are good, the sensors may be faulty and may need to be replaced. Nissan obviously sell them and make a good margin on them, hence my amazement that they didn't try flogging them already.