After many months of absolutely no problems, yesterday, Roon could not find the core. This resolved itself in ~1 hour followed by Qobuz stating it could not load the page.
Rebooted everything (incl. router), several times. Roon returned playing only my files (not Qobuz).
Asking if others have had (noted a post on Tidal…which I do not own) similar problem.
(Addendum: Not certain that I have diagnosed this, but I noted that 2 of four NEST thermometers went off-line, and the Roon and Qobuz access difficulty have resolved. Thinking this is an AT&T Fiber conspiracy).