Well Tim, Sorry I have no clue really. Somehow there is a possibility to create bad fbx files that crash the engine from, well i guess otherwise working geometry, but it’s not really easy to reproduce. I Think the case should be closed, i guess, because I also can’t really tell when this happens and how. Btw. Thank you for the autodesk FBX change list 
Also for really taking the time and working through it. But I can’t really reproduce it yet and don’t have the time to spend hours exporting and importing objects but maybe over time when the error repeats and I get a clearer grasp of it. But on the other hand, we are trying to opt for FBX 2016 export now because it’s 100% working there, except for the few poor ones that are sticking to 2014 at the office 
Anyway, really for trying but it’s just super hard to reproduce.