Not a Roon problem, but a hardware problem that is hard to diagnose. The power management implementation of Ryzen processors (microcode I believe) does not properly implement power saving. The net result is that the system hangs and crashes with watchdog timer expiry on higher numbered cores. You will see an error message on the screen, possibly in the system logs, that looks like “NMI watchdog: BUG: soft lockup - CPU#14 stuck for 22s!”
The solution is to turn off C-States in the motherboard bios (OC > CPU Features > Core C6 State = Disabled). This prevents the CPUs from being put to sleep. It increases power consumption a bit but my system stabilised after the change. The reason I am posting this here is that it took me a while to finally track down a solution. Hopefully this may save someone else the grief.