OK, I do have a fresh USB cable, I'll use that. I always keep at least one new cable in reserve in case of failure. A while ago my audio interface was playing up - yep, it was the cable.

You now are a certified Swaptronics technician

If this is happening as you describe when you are actually playing this is unlikely to be a USB power setting issue as Windows is receiving messages that should keep the hardware working together, not powering down. More likely a defective unit if it doesn't prove to be a USB cable issue. Least likely of these possibilities is a fault at the usb hub but still on the suspect list I suggest.

I sometimes use a little Masterkey keyboard with Pianoteq for checking presets and lazy doodling. Yesterday I was using it and it just stopped connecting to Pianoteq in the middle of playing - although the keyboard LED was still on. I tried the Pianoteq panic button, but the only way I could get the keyboard back was to restart Pianoteq. My first thought would have been 'dodgy USB cable', but I think it's unlikely in this case. It's a good quality cable and I haven't had any problems with it before. So I thought I'd better post the issue just in case it is a bug and it happens to anyone else. If it happens to me again I'll post an update.

First thing that comes to mind: does it happen with something else than Pianoteq ? Another VST plug-in in a DAW for example ?