Roon doesn’t get on nicely with NetworkManager which manages network devices and connections both on Ubuntu Desktop and Linux Mint. You have basically two options:
If your Roon core runs on a headless Linux server, I would simply install Ubuntu server which doesn’t suffer from this problem. I have done so myself.
The other option is to reconfigure your Linux so that it doesn’t use NetworkManager to manage network devices. Instead it can delegate to networkd which is default on Ubuntu Server.
Please refer to this thread for further illustration about the problem and a workaround:
Here you’ll find instructions on how to reconfigure Ubuntu Desktop:
@dylan and @noris know about the problem. Let’s hope the Roon QA team can come up soon with a solution to the root cause of this problem. I am sure there are quite a lot of users affected.