I don’t have a solution for you but I’m also having zigbee light issues for weeks while using HA 0.84.6 and couldn’t figure out why, or how to start troubleshooting. I would get error messages like these:
2019-01-18 21:33:46 ERROR (MainThread) [homeassistant.components.light.zha] light.living_room: Couldn't change brightness level: Message send failure: EmberStatus.DELIVERY_FAILED
2019-01-18 21:37:29 ERROR (MainThread) [bellows.zigbee.application] Failed to parse message (b'00120b0bd0d0d0d0') on cluster 6, because 208 is not a valid Status
2019-01-18 22:14:49 ERROR (MainThread) [homeassistant.components.light.zha] light.living_room: Unable to turn the light off: Message send failure: EmberStatus.DELIVERY_FAILED
2019-01-18 22:14:55 ERROR (MainThread) [bellows.zigbee.application] Failed to parse message (b'00170b0bd1d1d1d1') on cluster 6, because 209 is not a valid Status
Five minutes after getting these error messages, the lights suddenly start working again. I didn’t restart HA or anything. Go figure.
I think people are having similar issues in this post. I was going to mess with the entity registry until the problem resolved itself (for now). I hope you figure it out.