Basically any VST inserted into a ProChannel FX Chain Module is causing audio distortion if turned On/Off from within the FX Chain Module during playback.  If playback is stopped before turning a plugin On/Off no distortion occurs.  Also, if the plugin gui itself is open and I bypass or turn the plugin On/Off from its own gui, no distortion occurs.
 
Weirder.

I could be wrong here (hopefully someone else can chime in) but I think that might have to do with the latency that some plugins would be introducing in the audio chain. If you suddenly remove that latency (by turning a plugin off) sonar could be glitching because it throws off the timing of the audio signal. Just a guess on my part really.

Hi. My guess would have been the same as RSMCGUITAR's. It will also be dependent on which plugin you do this with.
All the best.

that ol' chestnut "during playback"