@shredsled I’m having the exact same issue. After the update to 2.6 everything worked fine for one album, then I went to bed. Update took 5 to 6 hrs to complete.
Today, roon and innuous see all my ripped and qobuz albums, each of my 3 endpoints, display all albums, notes and track selction yet won’t play a song. Volume is 100% and the progress bar does not indicate the song is playing, only flits back and forth along the line until I hit pause. Seems like for some reason, the song itself is not loading, or is not seen. I've never had this issue before. Did all the hard reboots you described and even switched my Zenith MK3 to Sense from Roon. Same issue. So I switched back to Roon core and nothing changed. Keep us posted on your resolution. I may have to start a repair ticket with Innuos as well.