Evening, I'm back with my issues again but the GREAT NEWS is that I finally discovered what the issues were.
 
When I was trying to work with soft synth projects I would get into the situation where Sonar would lose connection with the audio interface and just keep playing the timeline. Nothing would stop playback, not even shutting off the Fireface UCX and restarting it, clicking on the audio engine button had no effect. I was still able to save the project and navigate around the menus but I had to restart Sonar. Sometimes a precursor to that situation would be a loud pop. I submitted a couple of crash reports.
 
Anyway, I spent a day debugging on Friday.

Gathering everything that had been suggested on the forums I was convinced that this error was something on my PC interrupting either the CPU or trying to write to the same memory address, or some sort of graphics problem.
 
I made a long list of steps including trying different versions of the project file: All stock plugins and synths, no vst plugins, etc in a process of elimination.
 
No joy there! Issues appeared every session.
 
However I'd read somewhere that graphics drivers can cause problems. I was running the latest version of the AMD Catalyst GPU drivers so I uninstalled, cleaned the registry, and installed the standard out of the box driver from Windows. Loaded up the temperamental project and started tweaking. Eveything ok for 30 mins but then a crash, but not the unstoppable playback one!
 
Ok, checked Event Viewer and ProcMon (had it running during the project) and it gave me a clue. For whatever reason...maybe windows updates, I had a lot of scheduled tasks running around the time of the crash. After investigation I found I could disable all of these.
 
Since then? No crashes, no weirdness, flawless playback - for a whole day. I've never had this when playing with softsynth projects! I'm writing this after another 3 hours and no issues whatsoever. As I've been working on an audio only project for the last 6 months I' had given up playing with softsynth projects due to the crash frustration but now I've had the most creative time with all my energy focused on the creativity and not trying to 'fix' Sonar.
 
As a lot of you say - most issues occur because of something on your system and we're too quick to just say "it must be Sonar". As we all have different systems, some play nice but some present you with difficulties which feel like looking for needles in electronic haystacks.
 
Relief!
 
Cheers,
 
Mike