I tried to replicate the reported problem using MyInventory sample. I copy the snippet code of OnSourceItemsChanged and apply them into the ItemListViewModel of MyInventory sample; save the changes; and install the app to device.
Everything worked smoothly on device and emulator.

Could you please try to replicate this on MyInventory sample as I did and let me know the result.

Following information will be very helpful to determine what may cause the problem.

• Crosslight version -- I'm using Crosslight 3 Update 1
• Xamarin.iOS version -- I'm using Xamarin.iOS version 8.6.0.41
• the device -- I'm using iPhone 4s iOS 7.1

Look forward to hearing back from you.

Xamarin iOS 8.6.0.41?

I don't have this version. The latest stable version of Xamarin iOS is 8.4.0.47 in my download list. 

By the way, when I updated my Crosslight 3 to version Update 1 (Xamarin iOS 8.4.0.47 is used),  I found some bugs such as: 

• Unhandled Exception (System.MissingMethodException: Method not found: 'MonoTouch.UIkit.UITableView.RegisterNibForCellReuse') throws in OnViewCreated() in ViewController. 
• When changed to Unified API, the app cannot build : 'Failed to resolve "UIKit.IUISplitViewControllerDelegate UIKit.UISplitViewController::get_Delegate()" reference from "Xamarin.iOS, Version=0.0.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065" MessageInputSamples.iOS' .

Hello Leo,

For the instruction to upgrade to Crosslight iOS Unified and Xamarin iOS Unified, please check out our blog here.

FYI, the original error that you submitted actually have nothing to do with iOS Unified. The error was caused bythe Linker stripping out the classes required by Crosslight. The solution is quite simple, go to the Project Properties of the iOS project, select iOS Build, then put in the following syntax to the "Additional mtouch argument" textbox.

--linkskip=System.Core

Rebuild your project and run the app to your iOS device. Your apps should be working fine now.

Hope this helps.