Some Swarm Agents got stuck with Skylight Radiosity

Ok, all I can say is that my agents using Intel Xeons E5-2686W got stuck at Skylight Radiosity, 100% CPU usage.
My local Threadrippers and all render clients using Intel Xeons E5-2630 v3 or greater render fine.
UE 4.21 on Windows here.
Cold there be some SSE / MMX requirements of the CPUs are the cause?