I’m not using a ZEN15 - rather, I’m using less expensive TP-Link KP125 Wifi smartplugs.
However, I have run into a similar with my Whirlpool clothes washing machine. The power usage is all over the place.
The fix for me is to using a long finishing hysteresis, of 4 minutes below 6W. I came up with it by studying the consumption curve of the washer.
I came up with the 4 minutes because the “Tumblefresh” option of the washer spins once every 5 minutes, if enabled. I hadn’t enabled it in this particular cycle, though. Making the finishing hysteresis longer than 5 minutes would cause the finish action never to be executed if I had turned on that option in the washer, which I usually do, but forgot this time.