Unfortunately the Roon help site cut me off In mid-stream so that I could not complete the details of my problem. The problem was that after a power cut, I was asked to login again, but when I did this, I was told that I was already logged in. I was asked to go back but when I did that, I was again asked to login. I was stuck in this loop!
In the meantime, However, the issue resolved itself. Very mysterious but it is working now, so I can simply enjoy the music. Thank you for your interest.