Glad the Scaling up, processing and Scaling down fixed the problem - rememeber it for any operations like 'FollowMe' etc...
Some faces must be triangulated to form them - a three sided shape will also face but four points need not all be 'coplanar' and therefore might not 'face'. Some applications like triangulated faces for SUp exports anyway...
Many of the EEby.. tools triangulate the faces initially to ensure that they will 'face'. Then there is an option to erase coplanar edges later - this then removes any edges that are not needed to form a face so four or more sides are possible...
So when it asks you 'Erase Coplanar Edges' say 'Yes' and the triangulation will be removed wherever it can be... π€
First SU > DXF, then DXF2IGS. I found this, but don't use this. I understand that there is no fee for a working demo, but you must register. You can try it at your own risk.
I have my Model Info > Units set to return a whole of mm, so if the dimension is not a whole number SUp rounds it to the nearest whole number, but it adds a ~ to warn you that the figure is 'approximate'***...
1.0mm ==> 1
1.2mm ==> ~1
1.9mm ==> ~2
1234.0mm ==> 1234
1234.5mm ==> ~1235
***I find that I don't need to report dimensions etc to anything smaller than a 'mm'... You can if you like... π€