I don't have an answer, but might have clues...
 
I experienced the same thing about a week ago. Track meters would move and the TV scrolled as if playing back, but the only sound heard was an occasional click. Despite the silence, SPAN at the end of the master bus chain was pegged in the red. Eventually, SONAR would crash with sonarplt.exe shown as the faulting module - not a plugin.
 
No changes had been made to the project. One plugin had just been updated (MSpectralDynamics) so it was my first suspect. However, bypassing it made no difference, nor did removing it from the project. Then I began muting and then removing each bus plugin. The problem persisted even after removing all plugins from all busses. I closed and restarted SONAR, and still had the same problem.
 
I then rebooted the computer, and after that the project would load and play normally. Two days later, the problem returned. Altogether it happened on 5 occasions on 5 separate days, but always intermittent. Then I noticed that each time it occurred after having just had Chrome open playing a YouTube video. Experiments showed that that combination had a 50-50 chance of triggering the symptom. 
 
As I was writing this post, I just now tried to duplicate the problem again. SONAR is open on the first monitor and YouTube on the second monitor. I can switch between them at will and there are no problems with audio. What's changed? Just one thing: I've since installed the 23.5 SONAR preview. 

Yikes! I spoke too soon. I've just rebooted my computer and started up SONAR. There was no sound other than a couple clicks on starting playback. The cursor moves, track meters show activity, but no sound.
 
This project has three busses: drums, reverb and master, no plugins on any of them ATM. The meters on all three are pegged in the red and the peak readout says +9dB. Should be ear-splitting, but there is no sound.
 
Even after stopping playback, the meters remain stuck at full scale and remain there until the bus is muted, then they immediately jump back up as soon as they are un-muted. Somehow, a huge signal is making it onto all three busses. Must be drums, right? It's the only group that hits all three busses. Nope, it's not the drums.
 
Next, I started muting individual tracks. Muting one particular track made the bus meters return to zero. Aha! An unruly synth! But although it's a synth, it's frozen. That makes no sense. Being frozen, the synth (Omnisphere) has been unloaded and it's just an audio track as far as SONAR is concerned. Effects, however, were not frozen - so it must be an effect.
 
Next, I deleted the plugins on that track (Roth-Air and Pro-Q2). After both were gone, the project began playing again. OK! I thought, I'm an ace troubleshooter...but to my dismay the project continued to behave properly even after I used CTL-Z to un-do the plugins' deletions. In the end I had effectively done nothing, yet the project was now magically working again. I love magic when it's Penn & Teller, but I hate magic when I'm troubleshooting.
 
I then closed the project and re-opened it, and now the project plays fine. Go figure. The YouTube connection was a red herring. It's not a plugin or a synthesizer. It's gotta be some kind of internal math error, but one that's intermittent, and math errors are usually not intermittent. The exception is denormals.
 
 
 
 

bitflipper
Yikes! I spoke too soon. I've just rebooted my computer and started up SONAR. There was no sound other than a couple clicks on starting playback. The cursor moves, track meters show activity, but no sound.
 
This project has three busses: drums, reverb and master, no plugins on any of them ATM. The meters on all three are pegged in the red and the peak readout says +9dB. Should be ear-splitting, but there is no sound.
 
Even after stopping playback, the meters remain stuck at full scale and remain there until the bus is muted, then they immediately jump back up as soon as they are un-muted. Somehow, a huge signal is making it onto all three busses. Must be drums, right? It's the only group that hits all three busses. Nope, it's not the drums.
 
Next, I started muting individual tracks. Muting one particular track made the bus meters return to zero. Aha! An unruly synth! But although it's a synth, it's frozen. That makes no sense. Being frozen, the synth (Omnisphere) has been unloaded and it's just an audio track as far as SONAR is concerned. Effects, however, were not frozen - so it must be an effect.
 
Next, I deleted the plugins on that track (Roth-Air and Pro-Q2). After both were gone, the project began playing again. OK! I thought, I'm an ace troubleshooter...but to my dismay the project continued to behave properly even after I used CTL-Z to un-do the plugins' deletions. In the end I had effectively done nothing, yet the project was now magically working again. I love magic when it's Penn & Teller, but I hate magic when I'm troubleshooting.
 
I then closed the project and re-opened it, and now the project plays fine. Go figure. The YouTube connection was a red herring. It's not a plugin or a synthesizer. It's gotta be some kind of internal math error, but one that's intermittent, and math errors are usually not intermittent. The exception is denormals.
 
 
 
 

Internal math error ey? Damn, I should have pay more attention to math at school. haha.
I guess the thing with mine is that I can reproduce this issue 'fairly' consistently. Create a bus, add a compressor plug-in...might be okay. Copy that plugin to another bus and if it doesn't happen then, adding another compressor or dessor or whatever on a bus, will probably bring it on. I keep forgetting to try Noel's idea of turning of the audio engine before doing adding, so I'll make it a point to try that and report back. 
 
This has been happening for ages...well over a year on and off. I'm not always adding plugins on buses as some projects are already set up, so I don't need to add anything new...it's just when I do, it'll usually happen.
 
I watch quite a few tutes with people demonstrating these kinds of processes...adding plugin after plugin on buses etc. Maybe they don't show issues that occur during such demonstrations but there doesn't seem to be any issues for them doing so. 
 
I really hope I don't have to forever turn down my playback - or turn off the audio engine - each time I want to add a plugin on a bus.

The symptoms are classic for denormals. Even though the meters are pegged you hear nothing because its hitting invalid floating point values. These can be very tricky to find since its likely caused by some uninitialized variables in one of the plugins. So the result can vary depending what happens to be in memory at the time. That could be why you were able to repro with chrome and less likely otherwise.

Noel Borthwick [Cakewalk]
The symptom looks like some plugin is generating denormals due to an internal "crash" in the plugin. It can be hard to pin down such issues since it can occur randomly. When inserting plugins SONAR is streaming audio to them during this process so perhaps its a multithreading issue inside one of the plugins causing corrupted state.
If you can narrow it to which plugin causes it it would be easier to investigate potentially. Also check if turning off the audio engine before inserting the plugin avoids the problem.
PS: are you using sidechaining on the plugins in question?

Just a quick update...since last posting I've been getting into the habit of turning of the audio engine before adding any new plug-ins - apart from the pro console ones - and so far so good. This includes either track or buses. It's not like I add heaps of plug-ins every project as I already have a working template with set plug-ins but so far, adding any new ones and turning off the AE, seems to stop this issue from occurring. 
 
I'll post back to this in the event I have another issue whilst following this 'work-around'. 
 
Thanks for the suggestion Noel.

Just an update. I continue to turn off the audio engine before inserting any new plug-ins and it was going quite well with no issues, until a random 'meltdown' occurred. So unlike the other times when this occurred after inserting a plug-in, this just happened whilst working on various things...I was automating a delay on a voc track.
 
I've been receiving some follow-up emails from Jon Sasor - thanks Jon - Quality Assurance Cakewalk - which has been very supportive to receive BTW. He suggested turning off the 64 bit precision option as he reported that some plug-ins don't travel well through it. I don't know what the performance consequences of this might be - I haven't noticed anything at this point - but I'm trialing this to see if it arrests the random meltdown I described.
 
 
 

I guess you've tried various buffer sizes? To make things stranger, I use a Fireface UCX and have most of the plugins you mention. I use them all the time and always have 64 bit DPE on.

Sanderxpander
I guess you've tried various buffer sizes? To make things stranger, I use a Fireface UCX and have most of the plugins you mention. I use them all the time and always have 64 bit DPE on.

Yep, it's a strange thing to occur. It's a bit of a flow interruption to have to keep turning off the audio engine before inserting a plug-in...and sometimes I forget and I cringe for a minute and turn everything down in case I get that monitor overload which is not doing them any good I'm sure. 

I have a similar problem right now and using sidechaining on drums and synth parts. That might be worth a look at.
 

interpolated
I have a similar problem right now and using sidechaining on drums and synth parts. That might be worth a look at.
 

okay, thanks for that. I don't always set up for sidechaining but in the event I do and the issue occurs, I'll take note. So far with the AE off when inserting and the 64 bit precision option turned off, this issue hasn't re-occurred yet. It's hard to reproduce though but it does seem doing these 2 things help.