@Isaac_Spear - I suspect that you have a chain of HDMI devices: Nucleus → Anthem → Smart TV.
It’s probably the Smart TV that is causing an EDID handshake issue with the Nucleus. I had this issue when we replaced a Panasonic TV with a Samsung TV
I believe that I just have the Dr. HDMI device set to its simplest HD setting (1920x1080) - nothing to do with audio formats.