Repro of sizing issue reported by customer.

samples/Sandbox/MainWindow.axaml

@@ -1,4 +1,5 @@
 <Window xmlns="https://github.com/avaloniaui"
         xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
         x:Class="Sandbox.MainWindow">
+    <Button Click="Button_OnClick">Click me</Button>
 </Window>

samples/Sandbox/MainWindow.axaml.cs

@@ -1,8 +1,16 @@
+using System;
+using System.Threading.Tasks;
 using Avalonia;
 using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Layout;
 using Avalonia.Markup.Xaml;
+using Avalonia.Media;
+using Avalonia.Threading;
 using Avalonia.Win32.WinRT.Composition;
 
+#nullable enable
+
 namespace Sandbox
 {
     public class MainWindow : Window
@@ -17,5 +25,78 @@ namespace Sandbox
         {
             AvaloniaXamlLoader.Load(this);
         }
+
+        private void Button_OnClick(object? sender, RoutedEventArgs e)
+        {
+            var i = 20;
+
+            void Go()
+            {
+                var window = ShowWindow();
+                window.Opened += async delegate (object? o, EventArgs args)
+                {
+                    await Task.Delay(2000);
+                    window.Close();
+                    if (i-- > 0)
+                    {
+                        Go();
+                    }
+                };
+            }
+
+            Go();
+        }
+
+        private Window ShowWindow()
+        {
+            var window = new Window();
+            var heights = new[] { 491, 494, 554 };
+            var stack = new StackPanel();
+            stack.Orientation = Orientation.Horizontal;
+
+            for (var i = 0; i < heights.Length; i++)
+            {
+                var border = new Border();
+                border.Background = new SolidColorBrush(Color.FromRgb(200, 200, 200));
+                border.Width = 100;
+                border.Child = new TextBlock() { Text = i.ToString() };
+                border.Height = heights[i] - 5;
+                border.VerticalAlignment = VerticalAlignment.Top;
+                stack.Children.Add(border);
+            }
+
+            stack.Height = 1;
+            window.Content = stack;
+            window.VerticalContentAlignment = VerticalAlignment.Top;
+            window.SizeToContent = SizeToContent.Height;
+            window.CanResize = false;
+            window.WindowStartupLocation = WindowStartupLocation.CenterOwner;
+
+            void SetHeight(int i)
+            {
+                Dispatcher.UIThread.InvokeAsync(() =>
+                {
+                    stack.Height = heights[i];
+                });
+            }
+
+            async Task WhenLayoutReady()
+            {
+                await Task.Delay(176);
+                SetHeight(0);
+            }
+
+            WhenLayoutReady().ContinueWith(async _ => {
+                Task.Run(async () =>
+                {
+                    await Task.Delay(22);
+                    SetHeight(1);
+                    await Task.Delay(20);
+                    SetHeight(2);
+                });
+                Dispatcher.UIThread.InvokeAsync(() => { window.Show(); });
+            }, TaskContinuationOptions.ExecuteSynchronously);
+            return window;
+        }
     }
 }