update

Runtime/engine/UIWidgetsMessageManager.cs

 using System.Collections.Generic;
-using System.Runtime.InteropServices;
-using Unity.UIWidgets.service;
 using UnityEngine;
 
 namespace Unity.UIWidgets.engine {
         public static UIWidgetsMessageManager instance {
             get { return _instance; } 
         }
+
+        internal static void ensureUIWidgetsMessageManagerIfNeeded() {
+            if (!Application.isPlaying) {
+                return;
+            }
+            if (UIWidgetsMessageManager.instance != null) {
+                return;
+            }
+            var managerObj = new GameObject("__UIWidgetsMessageManager");
+            managerObj.AddComponent<UIWidgetsMessageManager>();
+        }
         
         string _lastObjectName;
 
         void UpdateNameIfNeed() {
             var name = this.gameObject.name;
             if (name != this._lastObjectName) {
-                this._lastObjectName = name;
+                this._lastObjectName = name;
 #endif
             }
         }

Runtime/engine/UIWidgetsPanel.cs

 
         protected override void OnEnable() {
             base.OnEnable();
+            UIWidgetsMessageManager.ensureUIWidgetsMessageManagerIfNeeded();
 
             //Disable the default touch -> mouse event conversion on mobile devices
             Input.simulateMouseWithTouches = false;