Thanks for your replys.
@Guilin Sun and @Lito Yap,
We have two licenses now. The problem occured when two users run their respective simulations at the same time, or one user run two simulations at the same time.
We had only one license a year ago. Back then, Running 2 simulations at the same time simply means that the simulation time would double. It was still working like that after we upgraded to 2 licenses, until maybe 1-2 months ago. We have been and is still using FDTD version 2022 R1.
No matter how many simulations are being run, CPU is being used ~100%. And I can confirm that the memory is not overwhelmed.
Thanks for your attention.