Unity 5.1.1 IL2CPP iOS device random crash

To support 64bit cpu, I upgraded my project from 4.3 to 5.1 and fixed some problems of ARC. However, when I run the build on my iPhone6 plus with iOS 8.4, the device random crash. I don't know whether it is still because of ARC problem. Anyone know anything please help me.

PS: I fixed my ARC problem by helping of this link: http://answers.unity3d.com/questions/917164/unity-5-iphone-builds-bad-access.html#

This is the log I got:

Thread 0 name: Dispatch queue: com.apple.main-thread

Thread 0 Crashed:

0 frontlinedefence 0x00000001009a7b4c Unity::SendMessageDirect(Object&, MessageIdentifier const&, MessageData&) (GameObject.cpp:1235)

1 frontlinedefence 0x0000000100a30ce0 Mesh::NotifyObjectUsers(MessageIdentifier const&) (Mesh.cpp:1273)

2 frontlinedefence 0x0000000100a30c00 Mesh::MainThreadCleanup() (Mesh.cpp:110)

3 frontlinedefence 0x00000001009a1644 delete_object_internal_step1(Object*) (BaseObject.cpp:435)

4 frontlinedefence 0x0000000100af9c88 CommitBatchDelete(BatchDelete&) (BatchDeleteObjects.cpp:132)

5 frontlinedefence 0x0000000100af9dbc BatchDeleteObjectInternal(int const*, int) (BatchDeleteObjects.cpp:205)

6 frontlinedefence 0x0000000100afa5bc GarbageCollectSharedAssets(bool) (GarbageCollectSharedAssets.cpp:1153)

7 frontlinedefence 0x0000000100b018fc UnloadUnusedAssetsOperation::IntegrateMainThread() (UnloadUnusedAssetsOperation.cpp:45)

8 frontlinedefence 0x0000000100afff50 PreloadManager::UpdatePreloadingSingleStep(PreloadManager::UpdatePreloadingFlags) (PreloadManager.cpp:416)

9 frontlinedefence 0x0000000100b00318 PreloadManager::WaitForAllAsyncOperationsToComplete() (PreloadManager.cpp:476)

10 frontlinedefence 0x0000000100b003f4 PreloadManager::UpdatePreloading() (PreloadManager.cpp:509)

11 frontlinedefence 0x0000000100afe8fc PlayerLoop(bool, bool, IHookEvent*) (Player.cpp:1687)

12 frontlinedefence 0x000000010090cc88 UnityPlayerLoopImpl(bool) (LibEntryPoint.mm:235)

13 frontlinedefence 0x00000001000f568c UnityRepaint (UnityAppController+Rendering.mm:246)

14 frontlinedefence 0x00000001000f5548 __51-[UnityAppController(Rendering) repaintDisplayLink]_block_invoke (UnityAppController+Rendering.mm:52)

15 libdispatch.dylib 0x00000001974d5990 _dispatch_call_block_and_release + 20

16 libdispatch.dylib 0x00000001974d5950 _dispatch_client_callout + 12

17 libdispatch.dylib 0x00000001974da208 _dispatch_main_queue_callback_4CF + 1604

18 CoreFoundation 0x000000018513b7f4 CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE + 8

19 CoreFoundation 0x000000018513989c __CFRunLoopRun + 1488

20 CoreFoundation 0x00000001850652d0 CFRunLoopRunSpecific + 392

21 GraphicsServices 0x000000018eabb6f8 GSEventRunModal + 164

22 UIKit 0x0000000189c62f3c UIApplicationMain + 1484

23 frontlinedefence 0x00000001000f1494 main (main.mm:40)

24 libdyld.dylib 0x0000000197502a04 start + 0