It was a mirage. Here is the now consistently repeatable behavior:

1. I open my project from a clean instance of Sonar on a clean rebooted system
2. Project is large,coontaining about 25 EWQL instruments. When fully loaded, which takes 5-6 minutes, Task Manager shows it consuming about 2.5 Gb of memory. A process called "System and compressed memory", which points to a file called ntoskrnl.exe, and will come into play later in these steps, hovers around 100 Mb RAM.
3. I start working in the project. 
4. After sometimes just a minute, sometimes longer, Cakewalk Fault Reporter opens and asks if I want to send a report, then Sonar closes. There seems to be no consistency around what I'm doing at the time the Fault Reporter opens. NOTE: Sometimes Sonar just crashes without the Fault Reporter.
5. At this point, BEFORE closing Sonar, I check Task Manager, and "System and compressed memory" is now at about 2-3 Gb RAM. Research has told me this is evidence of a memory leak.
6. I close Sonar, and the System and Compressed memory drops back down to 2-300 Mb RAM consumed, pointing to something in my project being the memory culprit here.

 
Steps tried:

• Windows Update
• Scan for malware
• Tried to repro with other projects, could not repro
• Removed recently purchased plug-in because it seemed to coincide with the onset of these problems, though I'm not sure of that, and the problems remain after having uninstalled it
• Saved project as a bundle and unpacked it as a new project. This seemed to make the problem take longer to occur, but otherwise no change in behavior. Also, in case this matters, the unpacked .cwp file is slightly LARGER than the original. (6.4 Gb vs 6.1 Gb)
• Re-opening the project without a reboot at this point causes a message to appear when loading the project, that the system is low on memory. I choose Ignore, because Task Manager tells me I still have plenty unused at that point.

UPDATE:: Removed all references to Midisporrt 2x2, seems more stable now, though System and compressed memory is up at 2 Gb again, so I feel a crash is just around the corner...
 
Closed project, left Sonar open thouggh, and System and compressed memory immediately went down to around 100 Mb again.

A 6 GB project file, how does that compare to your other projects? That seems unusually large for a cwp file.

Oops! I meant 6 Mb, not Gb! And that does track with the sizes of other projects.
 
More update: The crashing of Sonar coincides with this System and Compressed memory process in Task Manager. Whenever I get a crash, that process is up around 2 Gb RAM. Close Sonar (and even re-open the project afresh) and it's down to about 200 Mb. So I decided to open the project and start playing around with it while watching to see what I do to make it jump up and therefore facilitate a crash. What I discovered was that the System and compressed memory goes up when Sonar isn't even the active application on the computer! I did some playback, moved the now time around and the SACM (System and compressed memory) didn't budge much at all. Then I went on to do other things, (Chrome, Outlook, Evernote) and saw the SACM start to creep up, to about 275 Mb. I left the room, ate some bacon and fed the dog, and came back, and SACM was well over 1 Gb. In the time it's taken me to type this post, it has gone from 1.8 Gb to 2.4 Gb. I just now closed the project, did NOT exit out of Sonar, and now it sits back at 150 Mb. (Chrome, Outlook and Evernote are still open, btw. Sonar is definitely what's causing this memory leak)
 
Something in this project is causing the SACM process to consume oodles of RAM even when the computer is idle. In past years, with X3e, I knew that if I left a project open and came back to it the next day, it would often immediately crash on me, but this was before I knew about System and compressed memory in Task Manager, and it has seemed better for a while with SPro. 
 
Any ideas why this is happening?