[Dancake]

That hose should not be free to twist. It could be drawing in air which would stop the car from starting. The movement of the engine when starting could be enough to move the hose, causing the engine to start sometimes and not start other times. Diesel purge is a very effective fuel system cleaner, and it contains enough additives to keep the components in the fuel system well lubricated, but you need to make sure the HP pump doesn't run dry at all. A few seconds is all it takes to cause irreparable damage to a HP fuel pump.

In your case I would hazard a guess that there's air getting into the HP pump via the loose supply hose. The hose clamps onto an adaptor that's threaded into the pump. Hopefully it has just worked loose and the threads are fine. If so then it should just be a case of removing the hose, tightening the adaptor then refitting the hose.