Tangential, this Sculptris problem resembles my hair-tearing forays into using TurboCAD (2016) to edit OBJs for Poser.

I've just spent a week trying to 'top & tail' a 'kneeling pew' so I could 'book-end' several free-standing rows: A) chop kneeler off back row. B) truncate front row.
But, exporting such trivially 3D-sliced OBJs some-how scrambled the meshes, so that import to Poser created 'ST-TOS Transporter Accidents'. Bad as a sad FBX...

By accident, I found that importing edited OBJ to a different 3D program (eg $$ 3DOC) and promptly re-exporting usually de-snarled the mesh...

Worth a try ??

This is WIP of 10_metre span hall, to illustrate a story. I've timber trusses, opening clerestory windows, a Nantes-ish 'walking labyrinth' and a big, big central mandala, the latter to contribute Lovecraftian tentacles when the splinter sect's off-piste ritual 'Breaks Bad'...