Do you mean that Roon on your Macbook and iPhone doesn’t start or crash immediately, or that your NUC (I suppose using ROCK) does not boot at all?
I suppose it is most likely “just” the crash of Macbook/iPhone remotes and your ROCK does boot. In this case:
Go to the admin web page of your ROCK and check if it is up to date. Most likely it is not. Open your internet browser and try http://rock or if this does not work try http://rock.local. If this does not work either, use the IP address of the ROCK (which you can find listed in the connected network devices if you go to the admin web page of your router in a web browser)
The Roon Server Software version should be Version 2.0 build 1234 production. If it is much lower, you are a victim of this recent quite frequent issue:
Current releases of control devices / remotes crash when the Core is on certain older build numbers. Some Cores / ROCKs seem to have got stuck at an older build and then this happens. If all your remotes crash then you can’t initiate the update from the remote but you can trigger the update by going to the admin web page and clicking the Reinstall button for the Operating System: