When using the transition with the following code, the animation will freeze the first time it is triggered

[jiasss]

<Window.Styles>
    <Style Selector="Border.Animation">
        <Setter Property="CornerRadius" Value="5" />
        <Setter Property="Width" Value="300" />
        <Setter Property="Height" Value="300" />
        <Setter Property="Background">
            <LinearGradientBrush>
                <LinearGradientBrush.GradientStops>
                    <GradientStop Offset="0" Color="#ff0000" />
                    <GradientStop Offset="1" Color="#006688" />
                </LinearGradientBrush.GradientStops>
            </LinearGradientBrush>
        </Setter>
        <Setter Property="Transitions">
            <Transitions>
                <BrushTransition Property="Background"
                                 Duration="0:0:0.8"
                                 Easing="CubicEaseOut" />

                <TransformOperationsTransition Property="RenderTransform"
                                               Duration="0:0:0.8"
                                               Easing="CubicEaseOut"/>
            </Transitions>
        </Setter>
        <Setter Property="RenderTransform" Value="scale(1.0) rotate(-45deg)" />

        <Style Selector="^:pointerover">
            <Setter Property="CornerRadius" Value="8" />
            <Setter Property="Background" Value="#ff257868" />
            <Setter Property="BoxShadow" Value="0 0 10 3 #aa257868" />
            <Setter Property="ZIndex" Value="99" />
            <Setter Property="RenderTransform" Value="scale(1.2) rotate(45deg)" />
        </Style>
    </Style>
</Window.Styles>

<Canvas>
    <Border Classes="Animation"
            Canvas.Top="100" Canvas.Left="100" />
</Canvas>

[stevemonaco]

Try removing the BoxShadow. The first use is expensive, so that may be the issue.

[jiasss]

Thank you, it is indeed caused by that reason.