I'd try to check the export settings; if you use these steps, you can find some nearly invisible surfaces associated with the propellers:
Code: Select all
Then, hide the two hull halves. At this point, SelAll will report 8 surfaces selected. Details for these surfaces report a "quality" mesh, with two vertices, and zero faces (not a useable mesh), for each surface.
It gets more interesting, though, when you select them by mouse in the viewport, in which case it is reported that you have selected 424 or 848 surfaces (and Obj Props > Details will indeed think for a few seconds, before showing you a long list of properties for them). Selecting these and using ungroup, though, the same viewport selection now reports 8 surfaces selected, like SelAll did before.
So, I'm not sure what's going on with this file, but I'd would recommend sending it to McNeel, because it behaves very strangely.