Yeah, it's set to audio (mono)
I think I've located my problem area ...
I got a new audio interface (Roland Studio Capture) a while back and so far have not used it with this DAW. I set it up to record the Bass on Channel 3 and experienced the problem described. Today I re-configured for channel 1 and do not now experience the problem. I haven't yet figured why I had the problem on channel three and not on channel one - but the problem is probably "Cockpit Error". I'll follow-up when I have time.
Thank You for your patience and your help.