Engine cuts out after medium/long run

My brother who lives in mid Spain has a 2008 Skoda Octavia 1.9TDI, after a medium to long run of around 40 to 100 miles (summer or winter) and as he relaxes his foot off the accelerator the car will cut out, at first he said it happened after each service (fuel filter/housing ???) and then cured itself, but now it happens quite frequently. There is no evidence of exhaust smoke, there are no registered fault codes, it does not go into Limp Home mode, there is no evidence of fuel tank vacuum, the fuel pump is working continually, it never appears to misfire or run on 3 or less cylinders, there is no evidence of over heating. I am not sure if it has a DPF system, but with the motorway driving he does it should be clear anyway.The car generally takes around an hour before it will restart, but not every time.

Has anyone any experienced anything like this or have any idea what could cause this problem. There are no known outstanding recalls on this car, but manufacturers do not always tell the public about non safety related issues.

I would be grateful for any help and support.

Best regards

Ian McKay