ComboBox border and arrow disappearing after selection / while in focus

[ddesimio]

I am using an override of the MaterialDesignOutlinedComboBox to add some color. padding, and margin like so:
window xaml:

<ComboBox
        Name="MyComboBox"
        DisplayMemberPath="Name"
        IsSynchronizedWithCurrentItem="True"
        ItemsSource="{Binding Items}"
        HorizontalAlignment="Center" 
        SelectionChanged="ComboBoxChanged"
        SelectedIndex="0"
        Style="{StaticResource md_comboBoxStyle}"
        />

• The ComboBoxChanged function only enables a button if the index != 0

override xaml

<Style BasedOn="{StaticResource MaterialDesignOutlinedComboBox}"
           TargetType="{x:Type ComboBox}"
           x:Key="md_comboBoxStyle">
        <Setter Property="BorderThickness" Value="1" />
        <Setter Property="BorderBrush" Value="#2E79AB" />
        <Setter Property="Width" Value="200" />
        <Setter Property="Padding" Value="5" />
        <Setter Property="Margin" Value="5" />
</Style>

My problem is that after a selection is made, most of the ComboBox disappears while the window is in focus leaving just the text of the item selected - no more mouseOver functionality, border, arrow, or any indication that it is a ComboBox. If I click on another window they return but disappear again upon selecting the app window. I was unable to find any useful "InFocus" or related properties and the tutorials / examples I have done did not have this issue. Any help or advice would be greatly appreciated!

MaterialDesignThemes.MahApps 0.2.5 .NET 6.0