HI bill,
I had a similar problem when I started using kmotion cnc on a lathe, but it was not with fusion 360. I have another cam system, and if the kmotion cnc was set to display diameter mode on the X axis, the machine would choke on the arcs that came out of the cam system because they were being output in radius mode.
On my cam system it would not change the arc output even if I changed the cam system setup to diameter mode for some reason. This cam system is old and no longer supported, so I just run Kmotion cnc in radius mode, and no longer have any problems.
Hope this helps.
Andrew