Error running server update. Object reference not set to an instance of an object

Hi,

When trying to update from server version 4.8.20 to 4.9.17, I get following error :

Devices : 08/11/2022 12:50:13 : Event : Server : Error running server update. Object reference not set to an instance of an object. at BOSServer.Gateway.GatewayClient.Stop()
at BOSServer.BOSServerMain.Close()
at BOSServer.Helpers.UpdatesHandler.DownloadCompleted(Object sender, AsyncCompletedEventArgs e)

Any suggestion ?

Thank you