Seems like a mechanical failure of the AM466. When I try to turn it on, it makes a double clicking noise, but doesn't come on. When I looked inside the module, it looked like there's a little plastic arm that is supposed to push the ratchet and make it rotate. It looks like the little arm has broken off. I didn't examine the first one that failed, so I don't know for sure if it had the same problem. I bought them all from the same vendor on eBay, so I guess is could be a bad batch. The date code on the one I examined is 09K48. I don't know if there are different versions of the device or not. I doubt that my dehumidifier is pushing up to 15A.
I'll replace it and I'll see if I can modify my application so that it doesn't try to switch it on so frequently. What I'd really like is a 2-way module that I could query to see if it's turned on or not. With the AM466, you never know the true state of the device, i.e., whether it's really on or off.