FOUND IT!!!
OK, for whatever reason, CV was NOT activated.  We had to add a G64 to the front of the program to activate it.
After that, smooth curves!
I have since added the G64 to the initialization line in the Mach setup screen.  I thought checking the Constant Velocity button would do this?
We are still monitoring this, because randomly, CV has turned itself off again.
We can manually add the G64 to the program when we see this and all is well.
Not sure what happened to turn it off though...

You might need to increase the "Lookahead" lines from the default of 200.