"Monitor Sample" doesn't wake up properly

I was sampling some things and got up to handle some business. 2400 went into sleep mode. I came back to resume activities and I could no longer hear what I was sampling through the main speakers. All output routing goes through the mixer and nothing had changed.

I did notice, however, that monitoring through headphones was working properly. As soon as I exited sample mode and played the pads, sound came through the speakers again. I immediately went back into sample mode and the monitor was working perfectly. How is this possible??

There is no computer or powered monitors in my audio output chain. In other words, there are no other devices that go to sleep.

This happened again tonight with slightly different results. I left the machine in sample mode, came back a little later and the main outs are not outputting sound. However, I typically leave the headphones connected and they play perfectly. A quick restart and everything is back to normal.

Is there some kind of software control of the hardware outputs? I’ve only ever seen this behavior with computers, where something doesn’t wake up properly.