When that happens you can always open Task Manager and kill stereotool task/process and start ST again.
However that should not happen. Something is wrong with your hardware. Probably memory.
Thanks for taking the time to help me.
For some reason ST is not showing up in task manager. I've looked in Apps, Background processors and services.
I've seen it in task manager previously, but not now. The audio processing is definitely working, there are no glitches and peaks are tightly controlled. so ST is working away in the background somewhere.
Looks like I will have to restart the computer.
ps: love your work, Unreal Engine 2 is an excellent preset.