I think that would be in the Windows default device, right?
I was referring to the audio device assigned to a certain zone in Options>Audio.
Seems like a coincidence that 4 people called me this week to say they weren't getting sound out from their MC. Fortunately, they thought I was an MC deity when I had it fixed in under a minute. It's happened to one guy twice.
I wonder if it could be triggered by a sleep state in either the PC or their DAC if they leave it on and do not play audio through it?
So I've definitely seen this behavior before and it seems to be related to sleep/power transitions for me. Fortunately there's a workaround (for my case anyway).
If one of my DACs changes power states when my PC is awake, JRiver will sometimes "lose it" and then if I attempted to play to that zone, MC would auto reassign to a different available device. This was especially common when I have the WDM driver enabled, as the system tone resulting from the DAC appearing or disappearing would immediately trigger the issue by causing playback in MC! I also had the system setup to power off peripherals when the PC went to sleep. When the PC woke up, it would power on the peripherals, but because teh peripherals only turned off after the PC was awake, the peripherals "waking up" triggered a system tone leading to MC not seeing the DAC, etc. etc.
There are a few steps you can take to minimize the risk. One is to make sure that your DAC never changes power states while the PC is awake, which is ultimately what I wound up doing (the DAC no longer turns off with the other peripherals). Another step is to turn off MC's auto-reconfigure option, which prevents this kind of behavior to begin with. With the auto-reconf disabled, if I try to play to a non-existent audio output, I just get an error instead of a transparent reassignment.
This may not be your issue, but I thought I'd throw it out there as it was a source of frustration for me for a few months until I figured out the exact sequence of issues.