Wpf combobox never shows text of selecteditem

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C#

WPF

WPF ComboBox doesn't ever update text to SelectedItem's property, though SelectedItem changes on selection.

XAML:

<ComboBox  Margin="4 0 2 0"
           ItemsSource="{Binding XAxes}"
           SelectedItem="{Binding SelectedXAxis, Mode=TwoWay}"
           ItemTemplate="{StaticResource AxisCBTextTemplate}"/>

Template is:

<DataTemplate x:Key="AxisCBTextTemplate">
    <TextBlock Text="{Binding AxisTitle}"/>
</DataTemplate>

VM:

private AxisCollection _xAxes;
public AxisCollection XAxes
{
    get => _xAxes;
    private set
    {
        _xAxes = value;
        OnPropertyChanged("XAxes");
    }
}

private IAxis _selectedXAxis;
public IAxis SelectedXAxis
{
    get => _selectedXAxis;
    set
    {
        _selectedXAxis = value;
        OnPropertyChanged(nameof(SelectedXAxis));
    }
}

SelectedXAxis setter gets called, as well as OnPropertyChanged, but ComboBox does not show any text. List is shown as intended, no AxisTitle is lost.

What I have tried:

Changing ItemTemplate to DisplayMemberPath and SelectedValuePath:

<ComboBox  Margin="4 0 2 0"
    ItemsSource="{Binding YAxes}"
    SelectedItem="{Binding SelectedYAxis, Mode=TwoWay}"
    DisplayMemberPath="AxisTitle"
    SelectedValuePath="AxisTitle"/>

Adding an OnPropertyChanged("AxisTitle") to a VM code;
Different combinations of ItemTemplate, DisplayMemberPath and SelectedValuePath;
Leaving only

<ComboBox  Margin="4 0 2 0"
    ItemsSource="{Binding YAxes}"/>

causes an exception.