Hi, thanks for answering.
Since I use VScode, I set the number of threads in the settings of Julia extension. I did check with Threads.nthreads() after that and it was 4.
I also tried the distributed version before and it was okay. It was just the multithreading version. I guess it has something to do with some components of the optimizer Ipopt itself.
Thanks again for the detailed distributed version. It is quite lean compared to mine so I found it very useful.