I believe I have found an issue with OpenSCAD imports. I found it when working with a rather complex script, with many parameters, but I was able the to isolate the issue to this:
translate([1,0,0]) if (0) cube();
translate([2,0,0]) if (0) cube();
translate([3,0,0]) if (1) cube();
(As mentioned, the original script was more complex, with this appearing in a for loop with parameters controlling the if-sentences, but that turned out not to be important)
Importing this (or running it in the workbench) causes a "Multifusion failed" exception.
One can even simplify it to this case:
translate([1,0,0]) if (0);
translate([2,0,0]) if (0);
cube();
Same problem. If you remove the middle line, or the if (0) or the translate, it behaves all right. Pretty sure this is a bug, so I filed one: issue #3626