Roon application IDs are tied to the specific computer on which they are installed, with a unique ID created for each computer. Restores from Time Machine cause problems as to Roon there are now two computers using the same ID. You will need to completely uninstall Roon on Computer B and reinstall using a clean download from:
To completely uninstall Roon on a Mac, follow these instructions:
Reboot Computer B and reinstall using the MacOS link on the Roon Downloads page above.