Any version of Xamarin.Forms, the iOS version of the application crashes when attempting to apply a custom font "parameter descriptor cannot  be null"  

With this resource defined, and the OpenSans-Bold.ttf is in the Resources directory, marked as bundle resource...

<OnPlatform x:TypeArguments="x:String" x:Key="BoldFont">
    <On Platform="Android" Value="OpenSans-Bold.ttf#Open Sans" />
    <On Platform="iOS" Value="OpenSans-Bold" />
 </OnPlatform>

And using this code for the style (created from the Telerik login view template, with some modifications):

    <Style x:Key="LoginEntryStyle"
           TargetType="telerikInput:RadEntry">
        <Setter Property="TextColor"
                Value="{StaticResource DarkTextColor}" />
        <Setter Property="WatermarkTextColor"
                Value="{StaticResource LightBlueColor}" />
        <Setter Property="FontSize"
                Value="14" />
        <Setter Property="FontFamily"
                Value="{StaticResource BoldFont}" />
        <Setter Property="HeightRequest"
                Value="48" />
        <Setter Property="Margin"
                Value="0,0,0,16" />
        <Setter Property="BorderStyle">
            <Setter.Value>
                <telerikInput:BorderStyle BorderColor="{StaticResource LightBlueColor}"
                                          BorderThickness="1"
                                          CornerRadius="8" />
            </Setter.Value>
        </Setter>
    </Style>

When setting a custom Font, the RadEntry falls back on the default platform font family.

As a workaround you could set TextColor property of the Entry control.

I'm particularly wanting the "Assistive labels" features, which comes from Material design (click in the textbox, and the watermark becomes a floating label).  Like this:

https://www.syncfusion.com/xamarin-ui-controls/text-input-layout

Available in minor release 2018.3.1122. It will also be available in the R1 2019 release.

Available in minor release 2018.3.1109. It will also be available in the R1 2019 release.

When BorderColor is applied, it is still changed to the default one when the end user hovers over or focuses the control

IsFocused doesn't appear to work when it's bound to a property in an item template.

Introduce a MaxLength property. 

An example of such a feature is the Xamarin.Forms Entry control's MaxLength property: 

https://docs.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/text/entry#limiting-input-length 

In Android the OneWay binding to Text property is not working

Available in minor release 2018.2.821. It will also be available in the R3 2018 release.

If you apply a border with rounded corners and background color to RadEntry, the background exceeds the border.

Explicitly setting the Text property of the RadEntry to null results in NullReferenceException. This is not the behavior with the standard Entry control.

When setting a FontFamily on RadEntry, and the font family resource cannot be found, you'll be presented with an exception:

"Value cannot be null.
Parameter name: descriptor"

Stack Trace:

at UIKit.UIFont._FromDescriptor (UIKit.UIFontDescriptor descriptor, System.nfloat pointSize) [0x00011] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.8.0.20/src/Xamarin.iOS/UIKit/UIFont.g.cs:106 
  

On Android, when binding the Text value to a view model property, the value doesn't update.

Use the following to reproduce:

// VIEW

<Label Text="RadEntry" />
<telerikInput:RadEntry x:Name="MyRadEntry" 
                       Text="{Binding Username}" 
                       Margin="0,0,0,20"/>
        
<Label Text="Xamarin.Forms Entry" />
<Entry Text="{Binding Username}"/>

// VIEW MODEL

public class ViewModel : NotifyPropertyChangedBase
{
    private string username = "initial";
    private int counter;

    public ViewModel()
    {
        Device.StartTimer(TimeSpan.FromMilliseconds(500), (() =>
        {
            counter++;
                
            Device.BeginInvokeOnMainThread(() =>
            {
                Username = $"{counter}";
            });
                
            return counter < 100;
        }));
    }

    public string Username
    {
        get { return username; }
        set { username = value; OnPropertyChanged();}
    }
}


 Update: Available in R1 2018 SP release.