Entry value updated in VM but not in UI - Xamarin Forms

In my VM I am assigning value to CurrentItem.SecondValue when Toggle is checked it gets whatever value is entered in FirstValue Entry, but value is not getting updated in UI unless I refresh it/navigate between pages. When I debug it I see that CurrentItem.SecondValue is updated in VM. Any suggestions how it can be fixed?
XAML:

<renderer:CustomKeyEntry x:Name="FirstValue" Text="{Binding CurrentItem.FirstValue}" HeightRequest="40" WidthRequest="250" BackgroundColor="#FFFFFF"  Margin="15, 0" TextColor="Black" IsEnabled="{Binding IsThisEnabled}" ReturnType="Next" />  

<common:Toggle Text="{i18n:Translate Use_This_Number}" Checked="{Binding SecondValueIsFirstValue}" TextColor="Gray" HorizontalOptions="EndAndExpand" IsEnabled="{Binding IsThisEnabled}" Margin="0,0,10,0" />  

<renderer:CustomKeyEntry x:Name="SecondValue" Text="{Binding CurrentItem.SecondValue}" HeightRequest="40" WidthRequest="250" BackgroundColor="#FFFFFF"  Margin="15, 0" TextColor="Black" ReturnType="Next"/> 

ViewModel:

private Boolean _secondValueIsFirstValue= false;

    public Boolean SecondValueIsFirstValue
    {
        get { return _secondValueIsFirstValue; }
        set
        {                
            if (_secondValueIsFirstValue!= value)
            {
                if (value)
                {
                    CurrentItem.SecondValue = CurrentItem.FirstValue;
                    OnPropertyChanged();
                }                       
              SetProperty(ref _secondValueIsFirstValue, value);                                     
            }               
        }
    }

private ItemDTO _currentItem;
public ItemDTO CurrentItem
        {
            get { return _currentItem;}
            set { SetProperty(ref _currentItem, value); }
        }

 //DTO Class
 public class ItemDTO : INotifyPropertyChanged    
    {
        public event PropertyChangedEventHandler PropertyChanged;                     
        ....
    }