Inconsistent slicing

[ackbahr]

Hello!
I've been trying for DAYS to slice a model (originally downloaded from the internet)... Every time I would start a new session and import the same STL file the result would be different with mostly missing layers (sometimes one at a time, sometimes up to a dozen!) for parts of the object, or parts missing... Changing layer thickness only moves the problem to different layers or different parts of the object.
I tried remodelling parts and checking normals and all but finally had to settle for the least faulty of the results I had. This seems a bit rich for a paying piece of software such as Simplify3D!
I've joined my STL (gcode won't fit, but I've included images : one showing missing layers, the other showing missing part) so you can try and point something obvious I've missed or tell me "works perfectly well for me...
Of course it's a printer that usually works (and anyway I could already see in the preview that it was a mess) and a process that usually works...
Thanks for your help!

[S3D-Jason]

Those .stl files have a lot of mesh issues. There's holes, self-intersections, missing faces, and all sorts of bad stuff. Might be good to try repairing them first.

There's more info about this topic in the article below if you haven't read it yet:
https://www.simplify3d.com/resources/ar ... sh-errors/