I don’t understand, how exactly is your server machine configured?
Which NUC model and which operating system… ROCK, Windows…?
If Windows, is there anything else running on the NUC or just Roon Server?
If Roon Server loses connection, will other applications run fine (if any)?
Have you tried unplugging your entire system for a few minutes and rebooting it, lastly the server machine?
This will take a while I’m afraid. First of all there are holidays over Easter.