I have a similar issue with my C298. I am using a 12V trigger from my Denon AVR X4800H to wake the NAD. About once or twice a month one of the NADs channels would remain silent so I had to power cycle the C298 (while keeping the AVR on). This always fixed it.
I think in my case the reason was timing. The Denon AVR triggers the NAD C298 while it's preouts are still unstable. Sometimes there must be a small peak during this phase. I think there is some kind of protection logic in the C298 which detects a fault and disables the channel.
The fun part is that this can easily be fixed with a trigger delay box. A delay of 10 seconds between the Denon startup and NAD startup completely eliminated the random silent single channel for me.
Now this might be harder to achieve without using the trigger. But I am writing this in case anybody else is experiencing similar issues.
