Comment 31 for bug 1643383

the problem you are having is consistent with the change in default dpi from 90 to 96. However this change in the dxf export routine was made quite a while ago, so I am surprised that it is showing up now.

there are two things to check:
1. do a scan of your entire machine to make sure that there is one and only one version of dxf_outlines.py on your machine. Delete or rename or upgrade any old versions.

2. download the latest version of this file from:
https://gitlab.com/inkscape/inkscape/tree/master/share/extensions
make a backup of your existing version of this file and try the new one. It will be in the directory Inkscape\share\extensions\ or something similar to that.