JIT ExecutionEngineException on LLVM Compiled Production App

I have been using Xamarin.iOS for almost two years now and this just popped into my analytic queue for a application in the field:

Attempting to JIT compile method '(wrapper managed-to-native) System.DateTime:GetTimeMonotonic ()' while running with --aot-only. See http://docs.xamarin.com/ios/about/limitations for more information.

With a super helpful stack trace:

Stacktrace (most recent call first):

Module "System.Threading.Thread", line 0, in StartInternal

Module "System.Threading.Timer+Scheduler", line 0, in SchedulerThread

Why in the world is it attempting to JIT compile an already AOT compiled application?