Help diagnosing Energy tab showing phantom power draw from Fibaro FGS-223 device

Hi the energy tab is showing a constant draw/load/consumption of 374W from a device connected to S2 of a Fibaro FGS-223 relay (an electric towel rail element), even when the thing is off, whereas according to no power is being drawn (which is correct, because it’s off).

How can I diagnose what’s going on and where the fault lies?