你能提供一个最低复制码吗？那么我也许能帮上忙。
下面是我的测试代码：

using UnityEditor;
using UnityEngine;

// TestWindow1.cs
public class TestWindow1 : EditorWindow
{
    [MenuItem("Test/Window1")]
    static void ShowWindow()
    {
        var window = GetWindow<TestWindow1>();
        window.ShowModalUtility();
    }

    void OnGUI()
    {
        if (GUILayout.Button("Open Window2"))
        {
            var window = GetWindow<TestWindow2>();
            window.ShowModalUtility();
        }
    }
}

// TestWindow2.cs
public class TestWindow2 : EditorWindow
{
    void OnGUI()
    {
        if (GUILayout.Button("Open Window3"))
        {
            var window = GetWindow<TestWindow3>();
            window.ShowModalUtility();
        }
    }
}

// TestWindow3.cs
public class TestWindow3 : EditorWindow {}