Are the rads true radii or are they splines?
Can you post an example sldprt file for us to look at?
Do you have a model you could post up to evaluate? Also, I'd ask what version and SP you're running.
I don't have a timeframe (I simply don't know when it changed) but prior to running SW2016 we used to have spline issues that always haunted us. When we have a model that had basic geometry it went out to DXF without issue, but if the model we were working on has any surfacing any edges that touched that surface exported in splines regardless of the Export settings. This is not something we encounter any longer since upgrading to SW2016.
You can check your settings here as well, but like I mentioned this didn't always fix the issue.
Our primary problem was that none of our Wire EDM vendors could deal with splines. Polylines were optimal.
Also, the DWG/DXF version you save it as can have an impact. At some point AutoCAD used to not have ellipses, so anything saved in that version or earlier is converted to line segments. Sometimes ellipses and other entities give me issues with my nesting software, so I will occasionally save them as R12 as needed.