I am getting this error while updating discussion item's any property on SharePoint online. Error doesn't occur in case of document library and custom lists. Error Code is -2147024809 my code goes like this.
 public static SBUpdatePropsResponse UpdateProps(string siteCollectionUrl,string webUrl ,SBUpdatePropsRequest updateRequest)
{
    var updateResponse = new SBUpdatePropsResponse();
    var clientContext = Admin.GetAuthenticatedClientContext(webUrl);
    var web = clientContext.Web;
    var oList = clientContext.Web.Lists.GetById(updateRequest.ListID);
    var itemProps = updateRequest.ItemProperties;
    var itemUserProps = updateRequest.UserTypeProperties;
    var itemDateTimeProps = updateRequest.DateTimeItemProperties;
    ListItem listItem = oList.GetItemById(updateRequest.DocID);
    clientContext.Load(web);
    clientContext.Load(listItem);
    clientContext.ExecuteQuery();                   
    try
    {
        //Need to create a extra dictionary to save server time against property                
        var itemDateTimePropsLocal = new Dictionary<string, string>();
        foreach (var prop in itemDateTimeProps)
        {
            var dateTimeLocal = new DateTime(prop.Value, DateTimeKind.Utc);
            var temp = web.RegionalSettings.TimeZone.UTCToLocalTime(dateTimeLocal);
            clientContext.ExecuteQuery();
            itemDateTimePropsLocal.Add(prop.Key, temp.Value.ToString());
        }
        foreach (var userProp in itemUserProps)
        {
            if (userProp.Value != null && !string.IsNullOrEmpty(userProp.Value.ToString()))
            {
                var uservalues = userProp.Value as int[];
                //Handle for multi user property
                if (uservalues.Length > 1)
                {
                    var propValues = new List<FieldUserValue>();
                    foreach (var values in uservalues)
                    {
                        if (values > 0)
                            propValues.Add(new FieldUserValue { LookupId = values });
                    }
                    listItem[userProp.Key] = propValues.ToArray();
                }
                else
                    listItem[userProp.Key] = (new FieldUserValue { LookupId = uservalues[0] });
            }
        }             
        foreach (var prop in itemProps)
        {
            if (prop.Key.Equals("ContentType"))
                continue;
            if (prop.Value != null && !string.IsNullOrEmpty(prop.Value.ToString()) && prop.Value.GetType() != typeof(FieldUrlValue))
                listItem.ParseAndSetFieldValue(prop.Key, prop.Value.ToString());
        }
        foreach (var prop in itemDateTimePropsLocal)
        {
            listItem[prop.Key] = prop.Value;
        }
        listItem.Update();
        clientContext.ExecuteQuery();
        updateResponse.IsSuccess = true;
    }
    catch(Exception ex)
    {
        Logging.LogWriteLine("Failed to update list item properties", ex);
        updateResponse.IsSuccess = false;
    }
}