Ok I have some news:
I did update almost all the vehicle modules (DME, DSC, FZD, etc. etc.), and after fixing codes with tool32 and NCS Expert, I started the car with all the new SW available.
The car started perfectly in closed loop (AFR, Fuel Trims active on both banks), the rail pressure went up to 2500+ PSI at cold start and it eventually went back to 680-720 PSI at idle.
I gave it a quick ride, but eventually after a couple of minutes the HPFP dropped to 80-100 PSI, and limp mode was activated. It is important to say that this drop happened just after a deceleration (slowing down without using gas, AFR at 234.95 and Trims at 0).
I did several decelerations without using gas and not in all of them the pressure dropped like that.
I'm really confuesed, the HPFP seems to deliver the pressure without any problems (mechanically-wise speaking), but it seems that something cuts the pressure delivery to the fuel rail, and I don't know if there is an electronically controlled valve o something inside that could be having issues, or maybe there is a bad signal being delivered to the HPFP and reduces the pressure at minimum.
Please check my log and if you have an idea of what could be happening please let me know.
LOG:
Cold Start - New Flash
Thanks!