I have always had “Auto Monitoring” set to “Manual” (Preferences\VST) but today I set this preference to “Tapemachine Style”.
This mode is supposed to enable track monitoring when playback is stopped or when recording and disable it (so you can hear what is playing back on the track) during normal playback.
So I had the preference set to “Tapemachine Style” and was running off some mixes and noticed that the audio track currently selected in the project window was missing (muted) when I performed a mixdown.
Empty project. Add a single audio track, select it and drag in an audio clip and drop it on the track. Set the locators around the audio part.
in Preferences\VST set preference to “Tapemachine Style”. Back in the Project window you’ll see that the Monitor icon is now lit for the track.
Perform a mixdown. Result: silence.
If you manually disarm the monitor icon for the track the mixdown works properly. Surely it can’t be intentional that tracks with Monitor enabled are muted from a mixdown? It’s so easy to leave a track monitor enabled and not notice. Even if this were the design intention though “Tapemachine Style” disarms monitoring during playback so you would certainly expect it to do the same during a mixdown.