Mine doesn't start every time the first time I attempt cranking it. I now hold the key in the ignition position a bit longer than usual. Mine has new; HPFP__LPFP__fuel pump control module__injectors__6.6 bar fuel filter__plugs__coils__recent valve cleaning. And nothing has helped. I didn't replace all of those for solving its start-up issues. The fueling bits were done for resolving a low pressure issue from the LPFP at high load and revs...and for having a low specified pressure target from the HPFP at full throttle. Plugs and coils were swapped for the plugs being due and the coils had 150k miles on them.
I have recently read a post in the MKVGolfGTI UK forum. The owner, also was having start-up issues, who'd just done the timing chain and tensioner service, posted his start-ups are now crisp as it once was. I have yet done the cam timing service on mine, as I have planned on doing it at 160k miles. It has 157k miles at the moment. But I am hoping the start-up issue is resolved when I do the cam timing service. This may be something for yourself to consider...and would include; new chain & tensioner__new N205 rings__new N205__cleaning the N205 pick-up screen in the chain cover__disassemble and clean, or just replace, the cam phaser unit on the end of the exhaust cam.
There are more possibilities E.g.; runner-flap valves malfunctioning__throttle-body valve malfunctioning__other sensors may be reporting inaccurately to the ECU__fuel pressures are suffering__and who knows what else.
Fuel pressures and delivery may be the more likely cause, and it may require a thorough fuel pressure diagnosis. You'll want to conclude that the injectors, LPFP, fuel filter, injecotors and pressure limiting valve (FPRV) on the rail aren't the cause for fuel to escape from either the low or high pressure sides. This is one video link I share, which shows one determining where the system is losing pressure;
It basically is done so you disregard what the sensors are reporting...for they may be at fault as well. The gauge pressure can be compared to sensor data to verify they are reporting accurately or inaccurately to the ECU.
