I've converted .OBJs into .M2s countless times without any issues (weapons, helms, exteriors of buildings and NPCs). And I've tried importing WildStar weapons/armors/buildings but the same crash still occurs with each one. However, none of these models are over the vertices limit and convert to .M2 with no issue, so I'm kind of stumped with what the issue could be, except that the extractor may not convert them to .OBJ correctly or something along those lines.