When upgrading from 3.06 -> 3.0.8, a button makes Unity crash. It does not show any error and no crash logs are created.

Video of it happening, thought I don't know if it helps: https://files.catbox.moe/djagdk.mp4

It seems once I move my tooltip from the button it stops crashing, but it seems when I tried to add it back (out of playing) the editor crashed when the xaml was reimporting (?). My tooltip is a custom one that is made to follow the mouse.

public class SmartToolTip : ToolTip
{
private UIElement _targetElement;

    private TranslateTransform _transform;

    public static readonly DependencyProperty HeaderProperty = DependencyProperty.Register("Header", typeof(string), typeof(SmartToolTip));

    public static readonly DependencyProperty HorizontalPlacementProperty = DependencyProperty.Register("HorizontalPlacement", typeof(HorizontalPlacement), typeof(SmartToolTip), new PropertyMetadata(HorizontalPlacement.Right));

    public static readonly DependencyProperty VerticalPlacementProperty = DependencyProperty.Register("VerticalPlacement", typeof(VerticalPlacement), typeof(SmartToolTip), new PropertyMetadata(VerticalPlacement.Top));

    public string Header
    {
        get => (string)GetValue(HeaderProperty);
        set => SetValue(HeaderProperty, value);
    }

    public HorizontalPlacement HorizontalPlacement
    {
        get => (HorizontalPlacement)GetValue(HorizontalPlacementProperty);
        set => SetValue(HorizontalPlacementProperty, value);
    }

    public VerticalPlacement VerticalPlacement
    {
        get => (VerticalPlacement)GetValue(VerticalPlacementProperty);
        set => SetValue(VerticalPlacementProperty, value);
    }

    private void UpdatePosition(Point position)
    {

#if UNITY_5_3_OR_NEWER
//UnityEngine.Debug.Log($"X: {position.X}, Y: {position.Y}");
#endif
Point spacing = new Point(40, 40);

        Point offset = new Point(
            HorizontalPlacement == HorizontalPlacement.Left ? -ActualWidth - spacing.X : spacing.X,
            VerticalPlacement == VerticalPlacement.Top ? 0 : -ActualHeight);

        HorizontalOffset = position.X + offset.X;
        VerticalOffset = position.Y + offset.Y;
    }

    private void PlacementTarget_MouseMove(object sender, MouseEventArgs e)
    {
        if(_targetElement != null)
        {
            var position = e.GetPosition(_targetElement);

            UpdatePosition(position);
        }
    }

    public SmartToolTip()
    {
        Opened += SmartToolTip_Opened;
        Closed += SmartToolTip_Closed;
        ToolTipClosing += SmartToolTip_ToolTipClosing;

        Loaded += (s, e) =>
        {

        };
    }

    private void SmartToolTip_Closed(object sender, RoutedEventArgs args)
    {
        if (_targetElement != null)
        {
            _targetElement.MouseMove -= PlacementTarget_MouseMove;
            SizeChanged -= SmartToolTip_SizeChanged;
            _targetElement = null;
        }
    }

    private void SmartToolTip_ToolTipClosing(object sender, ToolTipEventArgs args)
    {
        if (_targetElement != null)
        {
            _targetElement.MouseMove -= PlacementTarget_MouseMove;
        }
    }

    private void SmartToolTip_Opened(object sender, RoutedEventArgs args)
    {
        if(PlacementTarget != null)
        {

#if UNITY_5_3_OR_NEWER
// UnityEngine.Debug.Log("Tooltip opened.");
#endif

            _targetElement = PlacementTarget;
            _targetElement.MouseMove += PlacementTarget_MouseMove;
            SizeChanged += SmartToolTip_SizeChanged;

            UpdatePosition(Mouse.GetPosition(_targetElement));
        }
    }

    private void SmartToolTip_SizeChanged(object sender, SizeChangedEventArgs e)
    {
        UpdatePosition(Mouse.GetPosition(_targetElement));
    }

    static SmartToolTip()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(SmartToolTip), new FrameworkPropertyMetadata(typeof(SmartToolTip)));
    }
}