I did only do some things with openHAB2 (my main system is (still) running OH 1.8 / 1.9)
But I know that this is a mix of old and new style, by defining a thing you should use a channel.
The items file should contain
Switch Switch_Staanlamp { channel="rfxcom:lighting4:238adf67:17733:command" }
Based on [SOLVED] Need help with manual RFXCOM thing configuration and assuming it to be correct 