Hello, I hope the following assists you.
If you haven't already done so have a diagnostic scan carried out on the PCM to check for stored fault codes and act on any that are evident.
There are a couple of common faults that can give the symptoms you describe.
If this happens after the car has been left for a time such as over night then check for air ingress into the fuel system, air will not allow the fuel pump to create enough pressure so you need to crank the engine for a long time before the air is expelled. The 2.0L diesel has a transparent pipe either from the injector return or where the feed pipe is clipped to the manifold so either will allow you to see air. It's unlikely to be this if there is no pattern to when the fault occurs but it needs checking.
Check the air shut off isn't sticking closed, this closes when the engine is switched off and then will open again when the engine stops. The EGR intake is close to the air shut of valve and deposits form on the shut off flap which build up enough to cause the shut off flap to stick. If you remove the intake hose at the inlet manifold you'll see the flap.
Another point is the crank sensor can cause problems usually if dirt or oil has gone on it, if this is the case this doesn't always store a code in the PCM.
There are other things that can cause the symptoms you describe but start with these points and let me know if I can advise any further.