A350 Airliner unable to climb

[Diamantfeuer]

Now, i dont know if i am missing something, but my A350 is unable to climb further than FL350. I did a flight from KJFK to EDDM, my first one since i bought MSFS2024, but i did this flight plenty of times in MSFS2020. But in this moment, i have 18 tonnes of fuel on Board and a GW of 182 tonnes. The plane is unable to climb further, it tries and maybe it would have made it after 5 hours or something. I goes up with 600 fpm, than loses speed and goes down and gains maybe 20 feet in the process, but after climbing like 700 feet after 10 minutes at 4x sim rate, it kinda stops. The recommended FL in the FMGC is FL413, and i have 18 knots of tailwind wich should'nt have impacted that either, because i have tried headwind and tailwind. Maybe i am just missing something but this has never happend before to me. Now again, this is only one flight, i havent tested this on any other flight, so it could just be one thing that is broken, but i am rather asking if this is a known issue, so yeah i still need to do more testing

Edited 6 hours ago by Diamantfeuer

[n1mmel]

What is your CI? Do you use Simbrief for your flightplan?