Reproduction steps:
1. Open the attached project.
2. Build and run it on an iOS or an Android device with il2cpp.
3.1. If asked to select "word level":
- Select Advanced.
3.2. If not asked to select word level:
- Go to Options > Current Level:... > Advanced.
4. Start tapping "Edit" and then "Cancel" buttons until you will see the "New Word" element.
5. Click "New Word"
6. Click on the input field that says "New Word".

Actual behavior:
- Crash.

Call stack (full call stack attached int the edit below):
...

• thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x58)
• frame #0: 0x000000010313c898 ...`::GetEventType() at IMGUIUtils.cpp:28 [opt]

frame #1: 0x000000010317cb38 ...`::Event_Get_Custom_PropType() [inlined] GetType at Event.bindings.h:50 [opt]
frame #2: 0x000000010317cb28 ...`::Event_Get_Custom_PropType() at Event.bindings.gen.cpp:566 [opt]
frame #3: 0x0000000104377f00 ...`::Event_get_type_mAABE4A35E5658E0079A1518D318AF2592F51D6FA(__this=0x00000001125c2200, method=0x0000000000000000) at Bulk_UnityEngine.IMGUIModule_0.cpp:1198
frame #4: 0x00000001043e3148 ...`::InputField_OnUpdateSelected_m32961891EC88E5E3BEFEF8A9C3FEB20789F437B0(__this=0x00000001125e1d80, ___eventData0=0x0000000114be3720, method=0x000000010a0b1c70) at Bulk_UnityEngine.UI_1.cpp:31199
frame #5: 0x0000000102da6304 ...`InterfaceActionInvoker1<BaseEventData_t46C9D2AE3183A742EDE89944AF64A23DBF1B80A5*>::Invoke(slot=0, declaringInterface=0x0000000109c8b060, obj=0x00000001125e1d80, p1=0x0000000114be3720) at Bulk_Generics_9.cpp:211
...

Reproduced with:
2018.3.0b1, 2018.2.7f1
iPhone 7+ iOS 11.1.1, iPod Touch 6 iOS 10.2.1
VLNQA00025, Xiaomi Mi 5s (MI 5s), Android 6.0.1, CPU: Snapdragon 820 MSM8996, GPU: Adreno (TM) 530

Note:
- The project doesn't move to 2018.1 and older Unity versions.
- Not reproducible in Editor, Desktop Standalone.
- Disabled Code stripping doesn't fix the crash.