Why is my Grid's first Child disabled

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WPF

Hello everyone.

I have a simple grid with 3 user controls in it.

<Grid Name="contentGrid" Grid.Row="1">
            <cntr:SourceDestination x:Name="sourceSelector" Opacity="0" Background="#FFC8D1F9"/>
            <cntr:BackupDestination x:Name="backupSelector" Opacity="0" Background="#FFD9FDDA"/>
            <cntr:Summary x:Name="summaryControl" Opacity="0"/>
        </Grid>

I swap these with with an animation function. This is working perfectly.
The trouble I'm having is with the user control in the grid. The first user control child controls cannot be accessed. It acts as if it's disabled.

I have tried focusing and enabling the user control to no avail. I have noticed if I change the order in which these user controls are added to the grid, it's always the first control that cannot be accessed.

Please help