Help please BMW 123d auto

[Tomndel20]

Bought the wife a 2008 BMW 123d auto been driving lovely but from time to time when sat at lights in gear it judders slightly like it's loosing power if sit too long it will cut out doesn't happen in park or nuteral. After driving for a few mins it goes back to normal. Not sure if this helps but dpf light will come on and go off not at same time as this happens. Basically if start the car drive for sometime it will come of but won't come back on again only once turned car off and on again and drove for some time really annoying me. I was thinking maybe dpf but if that was the case wouldn't it happen in park aswell hope for some advice cheers guys