Thanks @bar, @blurfl and @Gero
The file was made using a piece of software I backed on kickstarter in 2011 - sketchchair - so there was no JPG to SVG conversion - straight up vector file.
It was a cool project which seemed to die while still in beta - a shame as it is the perfect companion to a maslow cnc IMO.
I’ve just seen @blurfl’s post re the firmware fix - maybe that will resolve what is happening - I was planning to redraw the file in something else, but I’m 2/3 through this cut and matching the pieces would have been a bit of a muck around - would be good to get working as it is - strange how makercam interprets that line… it’s no different to any of the others