An actual Sonar problem, among all the other posts.
 
I've been mixing some demo songs today for a "retired" Nashville songwriter friend.  I'm mixing down mono (analog) tracks to a stereo track "Bounce to Track".  When its bounced to the stereo track, the Left channel is approx. 1.5dB lower than the right.  It has to be Sonar, and probably a setting, but I can't find it.  The Pan is set to "0" for all the tracks that I'm bouncing.  
 
Its not hardware as I have two recording interface units (an MOTU and a Focusrite) and it does it with both.
 
I had this previously and a monthly update seemed to fix it.  I tried going back to that update but it didn't make any difference.
 
I can compensate by adjusting the Left Channel level in Goldwave (audio editor) after I export the mixed and Ozone mastered but I shouldn't have to.    
 

As it's really difficult to visualise the problem you're having without actually seeing it, can I suggest some steps to take in order to troubleshoot?
 
I had similar problems back in the day with hardware mixers of varying makes, some better than others so I bought a reference test CD so that I could inject signals directly into the various channels for troubleshooting.
 
So how about getting some test signal recordings (wavs) at say 1KHz which should be recorded in mono and dropping them into a channel then bounce to stereo to see if something weird is happening with either your recording, your settings/project or it's an issue with your version of Sonar?
 
I'd also try the same steps using a plain default project from scratch, nothing else added to the project, just open template then immediately follow your process.
 
Over the years I've found that on occasion its been how I had my template set-up, a plug-in or on a very odd occasion, a bug in Sonar!
 
Generally, when I record bass and certain drum sounds, I always do it in mono and leave them that way, only allowing them to drop to stereo when they hit a bus as an example, such as a drum or effect bus.
 
Why would you want to bounce a mono track to stereo?
 
What happens if you leave the recording in mono and just set the interleave in stereo?
 
On occasion I might want to treat a mono signal with a stereo effect and so I leave the recording in mono but set the track interleave to stereo and drop an insert or send effect so that you get a mono signal effected in stereo so I suppose what I'm saying is what are you trying to achieve by doing this?  I have found that with certain recordings, because I can't get them to sound how I imagine them, I've had to be creative in Sonar and come up with an alternative workaround that produces the desired goal.
 
Hope that helps.  :-)

As these are song demos (13 songs) I didn't try to place instruments, left/right, etc.  Just bounced to stereo track to have two tracks.  They are the same so when it bounces and converts the mono to stereo both tracks should be equal.  
I have one SR-16 drum track, a bass track, a vocal track, a rhythm guitar track and finally either a pedal steel guitar or lead guitar track (actually very little lead instruments).  
 
I've done it this way since Sonar 6 and never had the imbalance in levels between left/right.  I had it earlier this year and the 2017.02 Sonar release fixed it.  I've done several CD projects since then and never noticed any level issues until this project. I tried rolling back to the 2017.02 but the problem was still there.  I'm back on current Sonar version.  To be exact, its 1.3dB difference, if that means anything.
 
I tried mixing to a mono track and then converting that to stereo but that didn't work either.
 

Sure, understood but the X series of Sonar was a quantum leap in functionality so I expect things in v6 were quite different from now and I've certainly experienced changes between 8.5 and Platinum.
 
Well, you may be right as it could be a bug in the summing/audio engine or something but the only way would be to try my suggestions and narrow down where it's going wrong to know for sure.
 
I had an oddity recently with a MIDI track within my own template and I just couldn't work it out.  In the end, I deleted that track and recreated it and guess what?  The problem has gone away and not returned since.  It therefore must have been a bug which happened during a certain moment while I was making my template but I'll never know for sure, only that I solved it.

I had an oddity recently with a MIDI track within my own template and I just couldn't work it out.  In the end, I deleted that track and recreated it and guess what?  The problem has gone away and not returned since.
 
This has been my experience with Sonar's quirky behavior too. Sometimes hitting undo does not resolve the weirdness. As I always have backups, I often will give up on the currant copy, and just open the back up and the weirdness will have disappeared with no explanation of why it was there to begin with... It is very rare that I have had to do it and I just write it off as software run amok. Had same thing this morning with Power Point. Couldn't copy paste txt files to a new presentation I was making. I gave up closed everything and started over and it worked just fine.. I think just like Sonar, I have hit some keystroke that sets off these weird behaviors. 
 
Your issue could be some setting has changed that sets up either the bounce or the new track. It will be one of those many hidden features you were not even aware existed. 

I'm going to do some more with this problem, but as the current project is done (only one I have scheduled until after the 1st of the year) I'll try some older projects that didn't have the problem and see if remixing causes the problem.  I'll report back tomorrow.
 

Did some testing this morning with an old project.  Mixes down OK so I have to assume there is something screwed up in the template I used for the demo song project.  However, I've used that same template in the past and no problems.  Murphy's Law has struck!
 
Solved "sort of"
 
Jack

fireberd
Did some testing this morning with an old project.  Mixes down OK so I have to assume there is something screwed up in the template I used for the demo song project.  However, I've used that same template in the past and no problems.  Murphy's Law has struck!
 
Solved "sort of"
 
Jack

There you go Jack!  That's what I meant when I wrote that I had a similar issue with a MIDI channel.  I isolated it by recreating the same settings on a default built-in template and it worked!  I then went back to my template, deleted the problem channel and recreated it, problem gone!  Never got to the bottom of it.
 
Glad the suggestions helped and you got a resolution. :-)

I'm going to play around with that template.  I did another demo song project last year for the songwriter and used the same template and it worked OK.  
 
I'll be going through the Groove 3 tutorials for Studio One 3 this month since I don't have anything scheduled until after the 1st of the year.  I'm good with Sonar as long as Windows doesn't break it, but when/if that time comes I'll be switching to Studio One 3.   
 
Thanks for getting in the right direction.
 
Jack