I am having a similar issue with Roon Server. After some period of time without playing music (typically overnight) I cannot find the remote core whenever I try to initiate playback from my IPad app. My system in actually an intel nuc with windows 10 pro.
Should I try the suggested method in comment #15 about rebuilding the database? Open to any feedback or suggestions on how to resolve as I currently have to restart roon server to reconnect to the core.