Audi A3 Engine Code BMN Warm-up Problem

Hi everyone, I have a small problem with an A3 and would like to know your opinions/experiences. Thanks in advance.
For the vehicle Audi A3, 2.0TdI, 16V, 170hp, manufactured in 06.2007, engine code BMN,
Regarding the problem: The vehicle starts perfectly in a cold state and runs smoothly without any loss of power, smoke, etc., but experiences slight to severe misfires at idle as the engine temperature increases, as if a cylinder suddenly cuts out. This is more frequent as the vehicle gets warmer. During driving under load, no noticeable issues are observed. In partial load operation up to 2000 1/min, the misfires are also noticeable during driving. If the engine is switched off while it is running and then restarted, it may take approximately 20 seconds or longer to get it running again.
Already renewed and inspected:
Parts comparison within the range of -0.7 to +0.7, PDE rebuilt, seals renewed and remeasured, cylinder head of PDE inspected (had slight inlet marks, but were worse), PDE wiring harness renewed, spark plugs renewed, cylinder head mixing tube renewed, fuel pressure to tandem pump checked, 2 bar desired, 3-3.5 bar at idle, electric fuel pump checked, approximately 0.5 bar, therefore OK, tandem pump renewed (Bosch), error still present, fuel pressure checked again, only 2 bar at idle, if you then squeeze the return line with a pair of pliers, the fuel pressure increases to approximately 4.5-5 bar, and the misfires at idle are gone, and the vehicle runs perfectly in its normal operating condition.. Now I suspect that the cylinder head has damage. Do you see it the same way, or do you have any other ideas about what could be the cause of the low fuel pressure in a warm engine? Okay, and the error memory is empty.

Thank you. Best regards, enzer

[Translating...]

Beim 16V sollten ja die PD Elemente 2 mal angeschraubt sein und eine konische Abdichtung zum Zylinderkopf haben. Meistens wird die konische Abdichtung im Zylinderkopf oval. MWB 23 mal kontrollieren.
Wenn man den Rücklauf zudrückt und der Druck steigt, dann sind die O-Ringe defekt, die hast du ja aber schon gewechselt. Montagefehler, O-Ring verletzt ?

[Translating...]

PDE s nochmals ausgebaut und O-Ringe überprüft. Messwerteblock 023 alle Zylinder ca. +23 +/-2 ich tippe mal stark auf Zylinderkopf defekt was meint ihr?