@Andrew_Webb – do remember that people who are sorry to hear about your issues are trying to help 
I did see that before asking my question. But I think the information you provided does not answer the question about whether your Core is connected via ethernet, does it? Sorry if I missed that, but I looked fairly carefully.
Sure, I don’t disagree with your perspective that none of this should be necessary. I wouldn’t have suggested a NUC if you hadn’t indicated yourself that you have thought of doing this.
[FWIW: I have purchased two lifetime licenses myself, and I would be furious if I were having the experience that you are having. Even though the UI issues that I have had since the 1.8 update are to me less serious b/c of my simple usage patterns, they still definitely affect how positively I see Roon and the Roon team that rolled out this update].
As compared with managing a Mac or Windows machine (even one that, in my case, was dedicated only to running Roon), I have found it very liberating to just run Roon from a device that is always on and that I can treat as an appliance. Roon users who run NUCs frequently mention this aspect as a positive.
Here’s the link. But looking at that thread again, the RAID SSD did not hold the Roon DB. So perhaps this is not relevant. In your place I would ask Roon Support about it directly if you haven’t already (they may not have mentioned it as a potential problem only because they didn’t notice that it’s RAID).
Hope you are able to move to a better Roon experience.