I've never had this issue with three custom build servers. With present custom build I'm rarely see anything above 5% usage in any particular core, this with Intel I9 processor. ATX board running Euphony OS.
I'd agree Roon forum not much good for troubleshooting, but then vast majority of issues are uniquely configuration based. Any issues I've had were due to operator error.My take is with Windows machines you better have powerful processor and max. services shut down or you may have issues.