Just a quick note to share how I fixed an annoying glitch. It might be helpful to someone.
I updated windows 10 a few days ago to the latest build. Upon relaunching Roon I realised I no longer had audio on my pc speakers (usb) or my headphones (via realtek out). Roon was working fine, audio devices were showing as properly enabled and my other network endpoints were working as normal. I could hit play sending audio to my pc speakers. Roon showed everything playing as normal but I had no audio at all on my local devices (those connected to my PC). I confirmed I had PC audio working well outside of roon so it was something isolated.
Cut a long story short, I removed / deleted all Roon instances from within the windows firewall. I then relaunched Roon and when prompted, I re-allowed it through the firewall. That fixed it.
Just wanted to mention this in case it helps anyone.