WPF Ribbon Headers not showing

Question

I meet a problem with Fluent Ribbon. I didn't change anything in XAML, but all Headers of my buttons disapeared. I don't know if it is a bug, or simply a shortcut to change appearance and Hide/Show headers.

Here is how looks the ribbon :

And how it looks like from now :

I tried to restart solution but nothing changed, same if I restart VisualStudio. But if I load a backup of solution last week all is working fine, that's why I think there is maybe a shortcut to make them appear/disappear?

Edit :

After additional tests I can add :

• Issue is present in both Debug and Release mode

• Problem is on all the solution, in all windows using Ribbon, not only that one

Answer 1

I finally decided to restart from a backup, and modify again the code file after file to finally find the issue (apologies to whom I said that I didn't modify xaml, didn't remember about that one, and didn't notice inmediately that this caused a problem).

In my App.xaml file I use the following style :

<Style TargetType="ToolTip">
  <Style.Triggers>
     <Trigger Property="Content"
        Value="{x:Static sys:String.Empty}">
       <Setter Property="Visibility"
          Value="Collapsed" />
     </Trigger>
     <Trigger Property="Content"
        Value="{x:Null}">
       <Setter Property="Visibility"
          Value="Collapsed" />
     </Trigger>
  </Style.Triggers>
</Style>
<Style TargetType="TextBlock">
  <Style.Triggers>
     <Trigger Property="Content"
        Value="{x:Static sys:String.Empty}">
       <Setter Property="Visibility"
          Value="Collapsed" />
     </Trigger>
     <Trigger Property="Content"
        Value="{x:Null}">
       <Setter Property="Visibility"
          Value="Collapsed" />
     </Trigger>
  </Style.Triggers>

I had to remove all the block and all is working again. But then I don't understand why Ribbon headers are influented by the style? Well I guess the headers are in textboxes, but they are not empty?