This happens to me quite often. I'll be working on a track, and in my case that means tons of editing and/or rerecording bits. At some point the track has enough and just stops outputing audio. It's still there, I can see the waveforms, I can see the meters moving, it just gets lost before it gets to the mains. It's not a matter of the outputs getting changed or anything like that, it usually happens when I stop recording, rewind, ctrl-z and hit record again (I do this a lot), but it has also happened to me while editing tracks. 
 
It's not hard to fix, I just clone the track and delete the old one. It's just annoying, and it's happened to me for several versions now. Anyone else have the same problem, or is it something unique on my end?
 
Darren

I've had problems similar to this while recording takes and I think I started a thread about it. It was confirmed... but it may not be the exact scenario you are having. IIRC I'd be recording takes then all of a sudden my echo output  would stop and/or previous takes were not getting muted and/or various other weirdness. It's been a long time though so I cannot remember the details. This was before I installed the X2a patch (I was on the Quickfix or maybe even the original build) and I have not done any intensive recording since I updated. If you haven't installed the patch though create a Windows restore point and install it to see if that helps. I'll try to dig up the thread. I think I was using the record keybinding (R) when this was happening and switching to using the transport module helped.
 
May not be related at all though but yes... I've had bizarre behavior when recording multiple takes.
 

That happens to me all the time, but I save, close Sonar, restart the PC, and it is fine.  Once in a great while, I can get things working just by clicking the Run/Stop Audio Engine icon on the Control bar. ( Itlooks like a waveform in the bottom left of the clock.)  This problem is extremely disruptive to the workflow, but you shouldn't have to lose your edits.
 
For me, some projects do this and others don't.  Sometimes freezing a soft synth solves the problem (even though I am a long way from running out of memory).  Having two projects open at once also can cause this.
 
Sorry for your pain but hopefully you can try saving and restarting so your work isn't lost.

yeah... this happens on occasion. I also restart the computer and interface from a cold boot to let them re-sync their communication signals.
 

Is this happening with a specific plugin/VST, or does it happen to random tracks of different types?