John
Something is amiss. None of the issues you are reporting should be happening. I would look at your overall setup making sure all your drivers are up to date and that Windows is also up to date. Many think that allowing the updates to Windows is a bad idea. I think that is a wrong headed notion. Those updates are to fix issues and add further security. I'm not saying you don't update but if you don't then that may be the problem.
John,
My system updates all of the time. One of the things I hate about Windows 10 is that it will download updates in the background while working on a project. In Windows 7 I had it set for notify so I could update between working on mixes.
My computer was built and is used for nothing else except Sonar and programs that work with Sonar.
Yes, I'll see if maybe my Focusrite or any other driver is up to date.
But think about it; I'm able to close the problem project, open a new one and side chain with no problem. No exiting of Sonar, no reboot. Yet, if I delete every single plugin from the problem project (which I did), reinsert two plugins, and try to side chain, the program crashes. There is no question in my mind that there is something in the background of Sonar that's already been corrupted and can not be repaired by resetting the mix to zero (no plugs). We can delete picture cache. Why can't we delete all background remnants from a wiped mix?
Other thoughts - Maybe there is an offending track? I haven't tried deleting tracks.