I've had the same problem w/ my AVR-1910. I originally solved it by disabling Dynamic Volume and some of the other audyssey settings, but the problem has since come back. Not sure if one of the kids changed a setting or what is going on. My current setup is OTA HD w/ Optical Out from TV (Sony XBR55850D) to the 1 optical input.
I notice when I check the "Status" on the Denon, it displays that I am only getting PCM audio, but the OTA HD broadcast says it's Dolby Digital.
The audio cuts out every minute or so for 3-4 seconds. If I change the optical IN to expect Dolby, I get no audio, even though the broadcast says it's Dolby. I have to set it to Auto or PCM, and from what I can tell is always receiving PCM. The TV support output PCM, Dolby, and DTS.
I'm tempted to reset the receiver, but then I'd have to setup and calibrate it all again. Any thoughts? When I search the issue, seems like a lot of Denon models around my model have similar complaints.
The TV is and Android TV, so if I am using one of the Android Apps (netflix, amazon, etc) there is no problem. It only comes up w/ OTA broadcasts.
As a work around, I have an Xbox one w/ USB tuner and using that for OTA TV for now, but I'd prefer the Sony Android TV interface for TV.