4.23 final here. On distributing Lightmass calculations I have a quite fast 16 cores Threadriper slave who is running UnrealLightMass.exe especially photon and Skylight Radiousity with ONLY a few CORES (20-30%). My workstation is almost hardware equal (the slave has a weaker NVidia Quadro than my GTX 2080) and renders about 30%-40% faster.
The culpit does not thermal throttle or anything like this. Otherwise on comparable work it’s rendering 3d frames with 3dsmax /Vray at normal speed.
Tried to raise processpriority, change cores assignment, restart, Windows updates, nothing helped.