[Solved] Issue with Prophet12 volume cutoff (midi?)

Once I switched to using USB midi the problem went away.
 
Hi all,

Just started using a Prophet 12 connected to Sonar midi in-out, audio into Focusrite interface, local is off on the synth.

Everything works fine for several minutes but now and then when adjusting any of the knobs on the synth I no longer get audio out from the synth.

The Prophet 12 voice lights are still switching on and off, midi us still working but there is no audio coming out of the synth.

Changing voice on the synth does not bring the sound back.

To get sound back I have to either click on midi reset in Sonar or turn the synth off/on.

Any ideas on how to troubleshoot this? Tomorrow I'll make sure the synth doesn't do this when its used stand alone.