https://lists.linuxfoundation.org/pipermail/accessibility-atspi/2016-October/000714.html

In our case, the launcher is started by the session manager, so it should already be running.

--- a/bus/at-spi-bus-launcher.c
+++ b/bus/at-spi-bus-launcher.c
@@ -257,6 +257,8 @@ session_manager_connect (A11yBusLauncher
       return FALSE;
     }
  
+  register_client(app);
+
         g_dbus_proxy_call (sm_proxy,
                            "IsSessionRunning", NULL,
                             0, 1000, NULL, is_session_running_ready_cb, app);
