I am adding this as it might be useful for someone. I had a "reduced engine performance" problem a few months ago and a couple of exhaust sensors were changed. This event I feel was different.
I had just filled up and then drove about 15 miles along the motorway at a steady 65/70. Then I came off at a junction and had to accelerate up a hill on a dual carriageway. I am not sure what happened next but suddenly lost power so changed down and found that I couldn't get more than about 2k rpm and the "reduced engine performance" message came up. I limped along to the next layby switched off and on again etc. Pulled out and still low power but I managed to complete my journey as long as I kept the revs and speed down. When I got to my destination I had a thought and undid the fuel cap and there was a huge inrush of air. The next morning the message was still there but the car seemed to be OK and after about 10 miles the message disappeared. During the rest of the day I periodically unscrewed the fuel filler and always got the inrush of air but the car drove OK. Today I had the filler cap apart and the valve is definitely working but presumably allowing too much of a vacuum to develop. I have now drilled a small hole in the centre of the valve.
This is a 2011 facelift with the later fuel cap which is a different design to the one on my son's 60 reg FL2. Car was serviced 3k miles ago and fuel filter replaced. 3 x FL1 2 manual + 1 auto
5 x FL2 4 manual + 1 auto
Now Discovery Sport P250 MHEV SE