I did not smoke anything, but it's highly annoying that if you post a bug report, someone is giving off-topic answers, and even insisting on doing so after you explain that's not the issue.
And as far as the image rendering on the models/processing page; this has nothing to do with manifold, but with zoom. If you zoom in or out you'll see all the thin walls are there. I think they deliberatelly not show one wall on a fairly zoomed out image, so you can see the structure. If you use zoom or walk around the model, the wall is there. These are all single thin walled prints. Probably by your 'repair' action you messed it up and made it more than thin wall (ie 2 perimeters wide).
ie now you don't see the wall:
and now (zoomed and rotated) you do:
About the model and manifold; it's totally not relevant. The model should just render to gcode fine, as it does in 3.11.
Please stop messing up a valid bugrequest by answering stuff no-one asked for.
Again; 3.11 processes these files to gcode fine. 4.0 crashes on it. This is a bug in 4.0. Even if the files would have been damaged, even then Simplify should not crash but produce normal errorhandling.
Please stop your efforts to undermine and frustrate this bugreport with offtopic nonsense.