To reproduce:

1. Download attached "IOSInt32Test.zip" project and open in Unity
2. Build for iOS
3. Deploy the Xcode project to the iOS device

Expected results: When Project is deployed everything works as Expected
Actual results: OverflowException is thrown in Xcode console:

"OverflowException: Arithmetic operation resulted in an overflow.
at System.Convert.ToInt32 (System.Decimal value) [0x00000] in <00000000000000000000000000000000>:0
at System.Convert.ChangeType (System.Object value, System.Type conversionType, System.IFormatProvider"

Notes:
- This issue seems to be related only with iOS
- This issue is not reproducible on Android (Mono and IL2CPP), Editor in iOS mode and Editor in Android mode
- Project is shared in Comments section

Tested with:
- iPhone 8 Plus, iOS: 12.0 - Reproduced
- iPhone X, iOS: 11.3.1 - Reproduced
- iPhone XR, iOS: 12.0 - Reproduced
- iPad Pro 3rd Gen, iOS: 13.0 - Reproduced
- VLNQA00277, Asus ROG Phone (ASUS_Z01QD), Android 8.1.0, CPU: Snapdragon 845 SDM845, GPU: Adreno (TM) 630 - Not Reproduced
- VLNQA00078, Motorola Nexus 6 (Nexus 6), Android 7.1.1, CPU: Snapdragon 805 APQ8084AB, GPU: Adreno (TM) 420 - Not Reproduced

Reproduced on Unity 2017.4.32f1, 2018.4.10f1, 2019.2.7f2, 2019.3.0b5 and 2020.1.0a6