I had a similar occurance following a long drive at 50mph avg speed, then cranking it up to 70mph in 4th. Just as the Regen finished I got DPF INSPECTION REQUIRED come up on the dash. Car still drove ok. When I got home I put Forscan on it and found error code
P243C:00.
After a visit to the dealer it was found to be the Exhaust Differential Pressure sensor (across the DPF) that sits left side looking aft under the heat shield at the rear of engine. Two bolts, two push on pipes and an electrical fitting. Just shy of £200. Though part was not cheap. It seems there was a problem with these sensors, but instead of changing them all they waited until one failed in warranty then changed it or charged the customer after warranty.