I would try a complete reboot of the Nucleus to see if it helps, by this I mean power off the Nucleus from the Web UI (using red power button in the top right-hand corner), disconnect the Nucleus power for 30 seconds and power back on.
If this still does not help, can I please ask you to share a screenshot of your Roon Settings -> About tab? The About tab is located in the top right-hand corner of the Settings screen, and you can share screenshots on this community website by using these instructions.