Mike - reading through this thread triggered another thought from me. It’s not the first time that there have been issues trying to get Roon working properly with a Denon + TV in a HDMI chain. See this thread for example:
And I started having problems when our old Panasonic LCD TV was changed to a new, state-of-the-art Samsung TV. Most of the time it was fine, but sometimes the Denon just would not see the Roon input. It all pointed to HDMI handshake issues caused by having a chain of devices (ROCK/NUC -> Denon -> Samsung TV). I finally cured it by a Doctor HDMI device between the NUC and the Denon. Not a cheap fix, but a quick one…
Edit: just as a thought: do you still get dropouts if you disconnect the HDMI cable between the Denon and the TV? I.e. use the Denon purely as an audio device. You may need to do a complete power-up of the Denon once the cable has been disconnected - i.e. coming out from Standby may still leave memories of the TV EDID details lurking in the Denon’s memory…