@masterprompt - from the very beginning of autocad (or at least from version 2.6 when I started using it) dxf file export has had struggles when attempting to export geometry that has any weirdness about it. every product since , autodesk or not, has the same problems.
lines laid over each other, intentional or not, can sometimes be one of those sources. (as can splines with bunched up control points and other factors. that means starting with clean geometry will give you the best chance of export success.
your sketch has curves doubled up on each other (every curve in this sketch does)-

in this particular case it would appear to at least partially be caused because you still have this setting turned on-

which I would highly suggest you go turn that off now. (whoever at AD who still thinks it's a good idea to have this setting turned on by DEFAULT really needs to have a stern talking to).
moving on, I couldn't really do anything with that sketch to get it to export properly. But, if I started a new sketch on an origin plane and projected the BODY (not the face) into the sketch it would export properly.
for some reason there is still some issue with export when projecting the face into a sketch. not sure why, perhaps a bug.
anyway, developing better sketch hygiene practices will greatly decrease the various difficulties, such as this and many others, you might be experiencing.
for example I randomly opened the "wall frame" sketch and checked this line-

and as you can see, there are 4 different sketch elements stacked on top of each other. it CAN be ok to lay sketch elements over each other. but needs to be methodical and intentional. other wise you'll end up with a mess that doesn't seem to want to behave at times.