Hi Martin,
I am only fledgling with ViaCad. I know you know it well. I just start with a default, blank ViaCad doc. The Step will have "stitching" options upon import to ViaCad. The STEp doesnt import for me in MoI.

I did find in ViaCad Some "Stitching gap parameters" that were set at .1 or something. This can be very large with this little disappearing fillets. Essentially, the re-stitching with the default ViaCad DOC and re-exporting made a good SAT from Viacad back to MoI. The mesh and surfaces object type were kindof random and not reproducable. Most of the time it reported as a solid too. But if it said "solid" and I chose "stitch", I would get a dialogue that says "all surfaces already seperated" or something like that. I'll try to do a video to see if I can show any of the anomolies.

Maybe a short description of how you originally brought the MoI model into ViaCad before the extra fillet work, and how you exported these files back out.

But this is all extraneous. Michael is looking at the underlying issues and may discover a bug to be fixed. I just jumped in as a means to help me understand the workflow with ViaCad also. If you want to continue with me, thats good for me, but now necessary. Talk later.