2011 TDI won't start on first crank?

2011 Golf TDI.

Over the past few months the car has not been starting the first time I try the ignition, or if it does, it takes 3-4 seconds of cranking. The strange thing is that if I turn off the ignition and immediately try again, it starts up normally. Further, if the engine has been running, the ignition issues disappear until the car is left sitting again overnight. I asked the dealer to test the battery and they said it's fine.

I suspect fuel pressure.
The pump should run long enough to get pressure after you switch off the key.
Try not cranking the engine for a few seconds first thing.
Maybe a leak in the fuel line.

I agree, I'm starting to suspect fuel pressure. Could this herald a HPFP failure? Or could it be something more benign? Should I insist the HPFP be replaced under the extended warranty?