OK, I've found some of the problems. First, the saved file was missing the ',"extension":"999"' clause that I see at the ends of smaller files I've saved. I added that and the saved map loaded.
Second, all of the props I added with the x axis mirrored loaded with the original rotation, so a bunch of the diagonal bits are going the wrong way and some doors are on the wrong side of the squares.
Several of the icons were listed as '\"visible\":false' which makes me wonder why they are still in there at all. Maybe lazy deletion? In any case, I tried a simpler repro map and the invisible icons didn't seem to break anything.
Finally, something I noticed while playing with this is that the prop in row 2 col 1 is just a tiny dot, which is not very useful, and the first two columns of row 4 are repeat triangles. I would have instead found it much more useful to have a thin top line to mirror the thin bottom line, but I'm sure everyone has their own preferences. It would be pretty great if we could load a different base props image though. =]