I know this has been discussed before but there has not been an answer. I have had a number of power outages this winter and each time the simple lighting quit working. I have let it go for 2 days and it still didn't work. I have found that rebooting and hard power cycle (unplug - replug) doesn't help. The only way to get it working is to do a shutdown and then power cycle.
This has been happening since I purchased the new version. I did not remember this problem with the old version of the hardware. I still have the old unit in my shop so today I took down a zigbee bulb like I use on my porches and set up a simple lighting rule to turn it on at sunset. I cycled power like a power outage and the light still came on at sunset. There appears to be an issue with the new units when they are not gracefully shutdown that a reboot doesn't correct. I have reported this problem last year but no resolution so I thought I would bring it up here to see if others have had similar issues. I would be willing to do additional testing if requested.
