I am evaluating the tool for possible usage at a University my Daughter is a Professor at. I did a simple mock up of a rectangle box with two rails inside, and two cutouts on either long side. The 3D view in Shapr3D looks correct. When I export a .stl file I get a model that fills in the cut outs, and the fill in extrudes a bit past the side walls on either side. The rails also have extra material below then as well. This should be a simple print, and should not be hard to get correct. Is it possible to email the file somewhere and have someone explain why this is happening? Please let me know.
This sounds like your Slicer software is adding supports, I would check if it’s enabled.
Also if you want STL looked at you can place it on Public File sharing like https://www.file.io/ and share the link.