the speed drops after some time

[TheBogeyman]

ok, thanks
Is it normal on NTLM hash? Maybe the card temperature affects it, 70 degrees, it is impossible to reduce it lower
4080*6 card and 128gb DDR5 RAM

If on win, install AFTERBURNER and undervoltat cards aka create profile with same gpu speed but 75mV lower voltage.
On Linux I don't know how to undervolt. 

But it is possible that hashrate drops.
Try to add -O (not zero but O) to hashcat string