Add context menu to RealtimeView component of Normcore. It allows to clean up Deprecated View references. Deprecated View references can cause issues with Unity's bug in serialization OnAfterDeserialize causing InvalidOperationException: EnsureRunningOnMainThread.

AddCleanupForRealtimeView.cs

using Normal.Realtime;
using UnityEditor;
using UnityEngine;

namespace Normcore.Editor
{
    public static class AddCleanupForRealtimeView
    {
        [MenuItem("CONTEXT/RealtimeView/Cleanup child views")]
        static void RealtimeViewCleanupChildViews(MenuCommand command)
        {
            ResetRealtimeViewChildViews(command.context);
        }

        [MenuItem("CONTEXT/RealtimeView/Cleanup ALL child views")]
        static void RealtimeViewCleanupAllChildViews(MenuCommand command)
        {
            var realtimeViews = Object.FindObjectsOfType<RealtimeView>();
            foreach (var realtimeView in realtimeViews)
            {
                ResetRealtimeViewChildViews(realtimeView);
            }
        }

        private static void ResetRealtimeViewChildViews(Object context)
        {
            var serializedObject = new SerializedObject(context, context);
            var propertyPath = "_childViews";
            var relativePropertyPath = "view";
            var serializedProperty = serializedObject.FindProperty(propertyPath);
            if (serializedProperty != null)
            {
                var serializedPropertyArraySize = serializedProperty.arraySize;
                for (int i = serializedPropertyArraySize - 1; i >= 0; i--)
                {
                    var arrayElementAtIndex = serializedProperty.GetArrayElementAtIndex(i);
                    var viewProperty = arrayElementAtIndex.FindPropertyRelative(relativePropertyPath);
                    if (viewProperty.objectReferenceValue == null)
                    {
                        serializedProperty.DeleteArrayElementAtIndex(i);
                    }
                }
                serializedObject.ApplyModifiedProperties();
            }
        }
    }
}