When you go above 64 threads, Windows puts the threads into processor groups. The software has to be designed to utilize multiple processor groups. Apparently Pix4DMapper isn’t “processor group aware”, so it will never use more than 64 threads. That’s why Puget’s testing showed improvement with SMT off for the 64 core Threadripper. 64 true cores is faster than 32 cores with SMT. And from what I can tell, Pix4DMatic behaves similarly.
I have a dual Epyc 16-core (32 cores/64 threads) that I upgraded to dual 32-core (64 cores/128 threads). I had to disable SMT to get the best performance in Pix4DMapper.
Hopefully this is in the development pipeline for Matic. I’ve given up hope for meaningful updates to Mapper.