Since the drum track in Groove Looper plays through Spark 2 via Bluetooth audio, it will be muted when the Spark 2 is connected as an I/O device via the USB cable.
See also:
Music Input Priority (Aux In / Bluetooth Audio / USB Audio)
To record the drum track in Groove Looper, you will need to connect the Line Out on Spark 2 to the input on an audio interface.