Do you happen to have any 3rd-party plugins loaded in these projects?
 
Bob Bone
 

Yes Bob, tonnes of them. But today Platinum refused to launch (just the program itself) before restarting. Something definitely not good here.

LJB
Yes Bob, tonnes of them. But today Platinum refused to launch (just the program itself) before restarting. Something definitely not good here.

That sounds like the previous instance hadn't exited completely.  Hung up on an audio or MIDI driver.  If this happens again, check for the Sonar process in Task Manager before you reboot. 

Will do thanks. Of course, I'd prefer if Sonar just did it's job :)

When Platinum locks up, whether it's on Exit, or Freeze Track, or whatever, sometimes Task Manager will close the 'Not Running' program, but it usually takes about six iterations before Sonar actually closes.
 
Close in Task Manager; then the notification window in Sonar opens; select Close The Program; back to Task Manager; back to Sonar; etc.
 
The MIDI icon usually remains.  After that I Restart.

BobF

LJB
Yes Bob, tonnes of them. But today Platinum refused to launch (just the program itself) before restarting. Something definitely not good here.

That sounds like the previous instance hadn't exited completely.  Hung up on an audio or MIDI driver.  If this happens again, check for the Sonar process in Task Manager before you reboot. 

As I speculated earlier: audio/MIDI driver not being released ... had that happen in X3 occasionally, but see it definitely more often in Braintree/Cambridge ...

I had it happen once in a while with my Delta66.  It hasn't happened even once with my Tascam interface.
 
And if the interface happens to be USB, the USB ports can be the culprit.

olemon
When Platinum locks up, whether it's on Exit, or Freeze Track, or whatever, sometimes Task Manager will close the 'Not Running' program, but it usually takes about six iterations before Sonar actually closes.

Might as well reboot and clean everything up.
 

I have seen this before, posted by others as well as experienced myself, and from recollection it seemed to happen mostly when there were 32-bit plugins loaded into a 64-bit Sonar, which then requires bridging software, such as Cakewalk's included BitBridge or commercially available JBridge.
 
I believe folks had success with unplugging or power cycling their audio interfaces and that would end up getting things to release.
 
For the above, it was something hanging up the audio interface drivers. (as far as I can recall)
 
Bob Bone
 
 
 

I'm experiencing the same issue. Hanging up upon closing projects. I also had some intense stuttering on playback today. Various instability issues happening seemingly out of nowhere :(