Honestly, I as very surprised to see that again Flow Simulation Users are limited to only two solvers in parallel even if they may have available 128 CPUs more.

This severe limitation  first came in 2013. Since then many others also write requests to SW (an old SPR should exists) to remove this limitation.
I called it severe for two main reasons:

1. It takes much more CPU time to run by 2 solvers than by , let say 64 solvers simultaneously. It is so because the speedup is not linear. I am attaching the Speed up curve of pump simulation (sliding mesh) for your reference with SW2017. You can see that above 4 CPUs the curve start saturated and practically there is no speedup above 16 CPUs.

2. A work around (for those who can open more than one SW Session at a time) is to open more SW Sessions and launch 2 Solvers from each of the sessions. However, it takes more User time and it is a BIG hassle to keep in one place the project files related to one and the same model.