Neil,

Had same issue about 6 weeks ago, Software update sussed it,

should see maximum 80-100mbar back pressure WOT in workshop.... (1.16psi - 1.45psi) for a clean DPF.

What fault codes do you have? if it has an aftermarket DPF is it possible it isnt getting hot enough / quick enough to carry out successful regen?

i never mess about with aftermarket DPF's.. we always obtain the original and regen before we proceed with diagnosing...