my understanding this correct it can cut out and it happened too me 2 days ago .if in wrong gear or low revs car can cut out

I was discussing a similar problem with my dealer earlier in the month and he shared a bulletin with me where Volvo states emphatically this "stalling" is not a Stop/Start system fault - the cutting out is the system operating to save the DMF from destruction. If the management system senses a stall (vehicle in the wrong gear, etc) it will, at the first chance, stop the engine.

How the system handles it from there depends on whether the driver's foot is on the clutch and whether the vehicle is moving not stationary. Volvo says although this may feel like the Stop/Start system failure, it isn't. That it is almost always a driver error. However there's a complication.

If the vehicle cuts out on you, place the gearbox into neutral, release the clutch, then put your foot under the clutch-pedal then pull upwards. If the pedal flicks upwards then the issue almost certainly lies with a damaged DMF - where the failing flywheel is dragging the clutch and causing the system to sense a stall.

Just had my DMF/clutch/slave changed for the second time in 25,000 miles.

Volvo apparently offers dealer warranty support on DMF till 2021.