I just heard the Jazz album TRIO of John Patitucci, Vinnie Colaiuta & Bill Cunliffe from TIDAL. At the end the message from Roon radio appeared that no similar music could be found, and Roon radio didn’t start. I think, that this is a bug of 1.8. I have a TIDAL and a QOBUZ subscription and a rather large local library, so that there must be plenty of “similar” music.
Besides this observation and some minor issues, I think that 1.8 is great.