Engine Mechanical problem
2003 BMW X5 6 cyl Four Wheel Drive Automatic 96000M miles

I have a 2003 X5 Diesel. About a year ago it was refusing to start after long runs until it had fully cooled down. It would turn over but not start, it also seemed unbalanced on turnover, like not all cylinders were firing. One diesel injector was changed as it wasnt switching off properly.

However I have had the same issue about 3 times over the last year. Its completely random, long journey or short journey it will crank but not turn over. I go back to it 30 mins later and all is ok. The fuel pump and injectors have been checked and no issue has been found.

Does anyone have a clue what this could be??
Any help is much appreciated.

Has the possibility of fuel contamination been eliminated? It may also be the fuel itself.