Ok, this was fun (not) to track down.
I have a document that originated in Rhino 5, curves are all in positive x, y space, exported DXF cuts just fine on both my lasersaur and Rabbit laser cutters.
Customer asked for a minor change, I’m now using Rhino 6, imported the 5 doc and made the change and exported DXF and both my laser cutters rejected the file.
It turns out the Rhino 6 DXF file has all the x values in negative space. Looking at the Object Description in 6 it shows all positive x, y locations. I cut-and-pasted the description in to a text file and have attached it and the .dxf.
[edit: I can’t share the 3DM file but I can export other formats or run tests as needed.]
[edit: Installed Rhino 5 and doing A/B tests. DXF exports are correct from 5 where 6 generates DXF files with negative X values.]
Version 6 SR15 (6.15.19164.21011, 6/13/2019)