I seem to be having a similar problem. On my Windows machines Roon no longer sees the local Windows PC as a zone. UltraRendu, iPhone and AVR all show up just fine.
In my case, I’m running the core on a Synology NAS. Cannot play to my Windows 10 Pro machine, which has a Benchmark DAC2-HGC dac attached. I updated the Roon client on another PC and have the same issue; Roon doesn’t see the Windows soundcard as an endpoint.