The script is unnecessarily complicated. For calling the GetMonitoredItems method, it is not necessary to have a subscription and monitored items, as the call result doesn't matter at all for this test. It is not even necessary to set input arguments, as only the number of methods that can be called in one service call are being tested.

Also, it might be worth checking if the "Server Test/NodeIds/Methods/MethodNoArgs" setting is configured and to use that method. Only if it is not configured, the GetMonitoredItems method should be used.