Thanks to the members who supplied us with info on perfhud and directx in debug mode. It has been a step forward but the cause of the problem is not known yet.
We are looking into getting a PC that already has the problem.
In the meanwhile, a suggestion from someone from our engine team: Can anyone try to turn on/off the "cool and quiet" option in the BIOS to see if this helps?
FYI: "Cool 'n' Quiet is a feature in AMD Athlon 64 that reduces the working frequency and Vcore when the processor is not under heavy load in order to lower the heat dissipation."
I will keep you posted if any other progress, though a solution seems to be close now.
