Starting from 2018.3.912.1 (was not able to reproduce in 2018.2.821.1 or earlier), loading charts on iOS crashes the device. This happens in the sample project SDKBrowser provided as well, when opening any of the Series charts (specifically the Vertical Bar which is what we have been using).
Stack trace of the crash:
System.InvalidCastException: Specified cast is not valid.
at Telerik.XamarinForms.ChartRenderer.iOS.ManagedChartDataSource.GetDataPoint (TelerikUI.TKChart chart, System.nuint dataIndex, System.nuint seriesIndex) [0x0002a] in <
94eed00967c543f5a13e0605d41bd543
>:0
at Telerik.XamarinForms.ChartRenderer.iOS.ManagedChartDataSource.GetPoint (TelerikUI.TKChart chart, System.nuint dataIndex, System.nuint seriesIndex) [0x0002c] in <
94eed00967c543f5a13e0605d41bd543
>:0
at (wrapper managed-to-native) ApiDefinition.Messaging.void_objc_msgSendSuper_IntPtr(intptr,intptr,intptr)
at TelerikUI.TKChart.set_XAxis (TelerikUI.TKChartAxis value) [0x00047] in <
44e9726d5f6f4545a2e89f7d32ff2c9f
>:0
at Telerik.XamarinForms.ChartRenderer.iOS.CartesianChartAdapter.UpdateXAxis (Telerik.XamarinForms.Chart.RadCartesianChart sourceOwner, TelerikUI.TKChart targetOwner) [0x0002e] in <
94eed00967c543f5a13e0605d41bd543
>:0
at Telerik.XamarinForms.ChartRenderer.iOS.CartesianChartAdapter.UpdateCore (Telerik.XamarinForms.Chart.RadCartesianChart sourceOwner, Telerik.XamarinForms.ChartRenderer.iOS.TKExtendedChart targetOwner, System.String propertyName, Telerik.XamarinForms.Common.IParentElement sourceOwnerRoot, System.Object targetOwnerRoot) [0x0003f] in <
94eed00967c543f5a13e0605d41bd543
>:0
at Telerik.XamarinForms.ChartRenderer.iOS.BaseChartAdapter`1[S].Update (System.Object sourceOwner, System.Object targetOwner, System.String propertyName, System.Object sourceOwnerRoot, System.Object targetOwnerRoot) [0x00000] in <
94eed00967c543f5a13e0605d41bd543
>:0
at Telerik.XamarinForms.Common.XamarinToNativeControlExtensions.Update[T,K] (T nativeElement, K xfЕlement, System.String propertyName, System.Object sourceOwnerRoot, System.Object targetOwnerRoot) [0x00031] in <
e2f1740c30914d7ea94cb9f8115f6f61
>:0
at Telerik.XamarinForms.ChartRenderer.iOS.BaseChartRenderer`1[T].OnElementAttached (T newElement) [0x00068] in <
94eed00967c543f5a13e0605d41bd543
>:0
at Telerik.XamarinForms.ChartRenderer.iOS.CartesianChartRenderer.OnElementAttached (Telerik.XamarinForms.Chart.RadCartesianChart newElement) [0x00000] in <
94eed00967c543f5a13e0605d41bd543
>:0
at Telerik.XamarinForms.Common.iOS.IosRendererBase`2[S,T].OnElementChanged (Xamarin.Forms.Platform.iOS.ElementChangedEventArgs`1[TElement] e) [0x0003f] in <
e2f1740c30914d7ea94cb9f8115f6f61
>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].SetElement (TElement element) [0x0012a] in <
0da03a4594684a9bbf17d4a99d39fbc2
>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].Xamarin.Forms.Platform.iOS.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) [0x00000] in <
0da03a4594684a9bbf17d4a99d39fbc2
>:0
at Xamarin.Forms.Platform.iOS.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) [0x00014] in <
0da03a4594684a9bbf17d4a99d39fbc2
>:0
at Xamarin.Forms.Platform.iOS.VisualElementPackager.OnChildAdded (Xamarin.Forms.VisualElement view) [0x0003d] in <
0da03a4594684a9bbf17d4a99d39fbc2
>:0
at Xamarin.Forms.Platform.iOS.VisualElementPackager.Load () [0x0001e] in <
0da03a4594684a9bbf17d4a99d39fbc2
>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].SetElement (TElement element) [0x000de] in <
0da03a4594684a9bbf17d4a99d39fbc2
>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].Xamarin.Forms.Platform.iOS.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) [0x00000] in <
0da03a4594684a9bbf17d4a99d39fbc2
>:0
at Xamarin.Forms.Platform.iOS.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) [0x00014] in <
0da03a4594684a9bbf17d4a99d39fbc2
>:0
at Xamarin.Forms.Platform.iOS.VisualElementPackager.OnChildAdded (Xamarin.Forms.VisualElement view) [0x0003d] in <
0da03a4594684a9bbf17d4a99d39fbc2
>:0
at Xamarin.Forms.Platform.iOS.VisualElementPackager.Load () [0x0001e] in <
0da03a4594684a9bbf17d4a99d39fbc2
>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].SetElement (TElement element) [0x000de] in <
0da03a4594684a9bbf17d4a99d39fbc2
>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].Xamarin.Forms.Platform.iOS.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) [0x00000] in <
0da03a4594684a9bbf17d4a99d39fbc2
>:0
at Xamarin.Forms.Platform.iOS.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) [0x00014] in <
0da03a4594684a9bbf17d4a99d39fbc2
>:0
at Xamarin.Forms.Platform.iOS.VisualElementPackager.OnChildAdded (Xamarin.Forms.VisualElement view) [0x0003d] in <
0da03a4594684a9bbf17d4a99d39fbc2
>:0
at Xamarin.Forms.Platform.iOS.VisualElementPackager.OnChildAdded (System.Object sender, Xamarin.Forms.ElementEventArgs e) [0x0000f] in <
0da03a4594684a9bbf17d4a99d39fbc2
>:0
at Xamarin.Forms.Element.OnChildAdded (Xamarin.Forms.Element child) [0x0000f] in D:\a\1\s\Xamarin.Forms.Core\Element.cs:332
at Xamarin.Forms.VisualElement.OnChildAdded (Xamarin.Forms.Element child) [0x00000] in D:\a\1\s\Xamarin.Forms.Core\VisualElement.cs:742
at Xamarin.Forms.Layout.OnInternalAdded (Xamarin.Forms.View view) [0x0001d] in D:\a\1\s\Xamarin.Forms.Core\Layout.cs:453
at Xamarin.Forms.Layout.InternalChildrenOnCollectionChanged (System.Object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e) [0x00078] in D:\a\1\s\Xamarin.Forms.Core\Layout.cs:443
at System.Collections.ObjectModel.ObservableCollection`1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedEventArgs e) [0x00018] in /Library/Frameworks/Xamarin.iOS.framework/Versions/Current/src/Xamarin.iOS/external/corefx/src/System.ObjectModel/src/System/Collections/ObjectModel/ObservableCollection.cs:263
at System.Collections.ObjectModel.ObservableCollection`1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedAction action, System.Object item, System.Int32 index) [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/Current/src/Xamarin.iOS/external/corefx/src/System.ObjectModel/src/System/Collections/ObjectModel/ObservableCollection.cs:338
at System.Collections.ObjectModel.ObservableCollection`1[T].InsertItem (System.Int32 index, T item) [0x0001a] in /Library/Frameworks/Xamarin.iOS.framework/Versions/Current/src/Xamarin.iOS/external/corefx/src/System.ObjectModel/src/System/Collections/ObjectModel/ObservableCollection.cs:196
at System.Collections.ObjectModel.Collection`1[T].Add (T item) [0x00020] in /Library/Frameworks/Xamarin.iOS.framework/Versions/Current/src/Xamarin.iOS/external/corefx/src/Common/src/CoreLib/System/Collections/ObjectModel/Collection.cs:71
at Xamarin.Forms.ContentPresenter.OnContentChanged (Xamarin.Forms.BindableObject bindable, System.Object oldValue, System.Object newValue) [0x0004e] in D:\a\1\s\Xamarin.Forms.Core\ContentPresenter.cs:88
at System.Runtime.CompilerServices.AsyncMethodBuilderCore+<>c.<
ThrowAsync
>b__7_0 (System.Object state) [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/Current/src/Xamarin.iOS/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/AsyncMethodBuilder.cs:1021
at Foundation.NSAsyncSynchronizationContextDispatcher.Apply () [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.16.1.24/src/Xamarin.iOS/Foundation/NSAction.cs:178
at (wrapper managed-to-native) UIKit.UIApplication.UIApplicationMain(int,string[],intptr,intptr)
at UIKit.UIApplication.Main (System.String[] args, System.IntPtr principal, System.IntPtr delegate) [0x00005] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.16.1.24/src/Xamarin.iOS/UIKit/UIApplication.cs:86
at UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x0000e] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.16.1.24/src/Xamarin.iOS/UIKit/UIApplication.cs:65
at SDKBrowser.iOS.Application.Main (System.String[] args) [0x00001] in /Users/username/Downloads/613233149246cf225930444fa4e25dc3_Telerik_UI_for_Xamarin_2019_3_913_1_Trial/Examples/Forms/SDKBrowser/SDKBrowser.iOS/Main.cs:14
This is happening on iOS Simulator 12.4, and on device on iOS 13.0. The current workaround is to stay on the old version of 2018.2.*, but this is not really a good workaround.