Steps to reproduce:
1. Download repro project "906975.zip"
2. Build Scene1 to iOS
3. On XCode add Security.framework library under "Unity-iPhone -> Build Phases -> Link Binary With Libraries" (if it is not there yet)
4. Build to iOS device
5. Press "Save" button.

Expected result: data is successfully serialized, information about it is outputted in Console.

Actual result: exception is caught:
System.InvalidOperationException: Operation is not valid due to the current state of the object
at System.Reflection.MonoMethod.MakeGenericMethod (System.Type[] methodInstantiation) <...>

Reproduced on: 5.3.7p2, 5.4.5f1, 5.5.3p2, 5.6.0p4, 2017.1.0b3 (with IL2CPP)
Did not reproduce with Mono2x

Note: could not test on Android because of build errors