Буквы частично не отображаются

Без какой либо закономерности иногда исчезают буквы в приложении. Ситуация не зависит от версии ОС или устройства, появляется везде без видимых причин.

Мой XAML:

<StackLayout  BindableLayout.ItemsSource="{Binding EDocuments}">
    <BindableLayout.ItemTemplate>
        <DataTemplate>
            <SwipeView Grid.Row="0" BackgroundColor="Transparent">
                <SwipeView.LeftItems>
                    <SwipeItems>
                        <SwipeItem Text="Акти"
                            IconImageSource="{extension:ImageResource DriverHelper2.Resources.Icons.eActFttn.png}"
                            BackgroundColor="Transparent"
                            Command="{Binding Source={RelativeSource AncestorType={x:Type view:EdocumentsListViewModel}}, Path=ETTNsActsCommand}"
                            CommandParameter="{Binding Id}">
                        </SwipeItem>
                    </SwipeItems>
                </SwipeView.LeftItems>
                <Frame CornerRadius="10" BackgroundColor="#66000000">
                    <StackLayout Orientation="Vertical" HorizontalOptions="FillAndExpand">
                        <StackLayout Orientation="Horizontal">
                            <Label Style="{StaticResource LabelTitleFontSize}" Text="Номер документа:" ></Label>
                            <Label Style="{StaticResource LabelFontSize}" TextColor="White" Text="{Binding DocumentNum}"></Label>
                        </StackLayout>
                        <StackLayout Orientation="Horizontal">
                            <Label Style="{StaticResource LabelTitleFontSize}" Text="Точка вивантаження:" ></Label>
                            <Label Style="{StaticResource LabelFontSize}" TextColor="White" Text="{Binding UnloadPoint}"></Label>
                        </StackLayout>
                        <StackLayout Orientation="Horizontal">
                            <Label Style="{StaticResource LabelTitleFontSize}" Text="Кількість місць:" ></Label>
                            <Label Style="{StaticResource LabelFontSize}" TextColor="White" Text="{Binding PlacesTotal}"></Label>
                        </StackLayout>
                        <StackLayout Orientation="Horizontal">
                            <Label Style="{StaticResource LabelTitleFontSize}" Text="Загальна вага:" ></Label>
                            <Label Style="{StaticResource LabelFontSize}" TextColor="White" Text="{Binding WeightTotal}"></Label>
                        </StackLayout>
                        <StackLayout Orientation="Horizontal">
                            <Label Style="{StaticResource LabelTitleFontSize}" Text="Статус:" ></Label>
                            <Label Style="{StaticResource LabelTitleFontSize}" TextColor="White" Text="{Binding EDocState.StateName}"></Label>
                        </StackLayout>
                        <StackLayout Orientation="Horizontal">
                            <Label Text="Перелік товару:" VerticalTextAlignment="Center" TextColor="Yellow" FontSize="22"/>
                            <Image 
                            WidthRequest="50" 
                            HeightRequest="50" 
                            HorizontalOptions="EndAndExpand" 
                            Source="{Binding HideImagePath, Converter={StaticResource StringToImage}}">
                                <Image.GestureRecognizers>
                                    <TapGestureRecognizer Command="{Binding HideEDocs}" NumberOfTapsRequired="1" />
                                </Image.GestureRecognizers>
                            </Image>
                        </StackLayout>
                        <StackLayout  BindableLayout.ItemsSource="{Binding Specifications}" IsVisible="{Binding IsHide}">
                            <BindableLayout.ItemTemplate>
                                <DataTemplate>
                                    <Frame CornerRadius="5" OutlineColor="#c3c3c3" BackgroundColor="White">
                                        <StackLayout>
                                            <StackLayout Orientation="Horizontal" HorizontalOptions="FillAndExpand">
                                                <Label Style="{StaticResource LabelTitleFontSize}" Text="Найменування:"/>
                                                <Label Style="{StaticResource LabelFontSize}" Text="{Binding Name}"/>
                                            </StackLayout>

                                            <StackLayout Orientation="Horizontal" HorizontalOptions="FillAndExpand">
                                                <Label Style="{StaticResource LabelTitleFontSize}" Text="Тип:"/>
                                                <Label Style="{StaticResource LabelFontSize}" Text="{Binding TypeOfPackaging}"/>
                                            </StackLayout>

                                            <StackLayout Orientation="Horizontal" HorizontalOptions="FillAndExpand">
                                                <Label Style="{StaticResource LabelTitleFontSize}" Text="Вага:"/>
                                                <Label Style="{StaticResource LabelFontSize}" Text="{Binding GrossWeight}"/>
                                            </StackLayout>

                                            <StackLayout Orientation="Horizontal" HorizontalOptions="FillAndExpand">
                                                <Label Style="{StaticResource LabelTitleFontSize}" Text="Кількість місць:"/>
                                                <Label Style="{StaticResource LabelFontSize}" Text="{Binding NumberOfSeats}"/>
                                            </StackLayout>
                                        </StackLayout>
                                    </Frame>
                                </DataTemplate>
                            </BindableLayout.ItemTemplate>
                        </StackLayout>
                        <StackLayout Orientation="Horizontal" Padding="0, 15, 0, 0">
                            <Label Style="{StaticResource LabelTitleFontSize}" TextColor="Yellow" Text="Вибрати:" />
                            <Switch Scale="1.5" IsToggled="{Binding IsChecked}"  OnColor="LightGray" HorizontalOptions="EndAndExpand" ThumbColor="{Binding SwitchColor}" />
                        </StackLayout>
                    </StackLayout>
                </Frame>
            </SwipeView>
        </DataTemplate>
    </BindableLayout.ItemTemplate>
</StackLayout>  

Шрифт для всех Label:

<Application.Resources>
    <ResourceDictionary>
        <local:StringToImageSourceConverter x:Key="StringToImage" />
        <local:ImageResource x:Key="ImageResource" />
        <Style TargetType="Label">
            <Setter Property="FontFamily" Value="BanderaFont" />
        </Style>
    </ResourceDictionary>
</Application.Resources>  

В файле Assembly.cs:

[assembly: ExportFont("BanderaProMedium.ttf", Alias = "BanderaFont")]