This issue has been closed as 'Won't Fix' due to an extended period of time without updates. If this issue is important to you please let us know by posting on the AnswerHub or UDN, and Epic will re-open the ticket for further review.
Edit MattK: This seems like more of a cooking issue than an fbx issue. The crash is related to nav collision
When adding a FBX import into your project, if you do not close the project out and open it back up, it'll cause the project to crash when it's launched onto an iOS, Android or Windows. But it'll also crash in a packaged project for Android.
Work Around:
1. Import FBX (Successfully)
2. Save Project
3. Close Editor
4. Reload Editor
5. Deploy to Mobile
1. Create a new project
2. Import FBX into the project
3. Launch onto iOS or Android
Results: The project crashes when it launches
Expected: The project should load without crashing.
Head over to the existing Questions & Answers thread and let us know what's up.