I’m in US but have been following these forums for a year, haven’t noticed mention of Greenwave Powernode. Are these popular/mainstream zwave devices, or a “discount” type product? I did a search here and found at least one other person is having the same flashing issue with them…
Maybe try a more mainstream device (are these popular in UK: Aeon, Fibaro?) and see if you have better results? Here in US I have had better luck with GE and Aeon switches/plugs than I have had with cheaper Enerwave switches.