I’m somewhat new to SmartThings, I got the Hub v2 and a number of devices a few months ago and everything has been working great so far. But this morning when I woke up I noticed that the routines for my living room lights didn’t run so I checked my SmartThings app and all my devices were listed as “Unavailable”. I reset the hub and some of the devices came back but my three Cree Connected bulbs (ZigBee devices) are still unavailable. The strange thing is that I can still control them using the app, and I can also use my Amazon Echo and my Harmony remote to control them too. I did some searching online and it sounds like there are possible issues with ZigBee and WiFi interference (https://support.metageek.com/hc/en-us/articles/203845040-ZigBee-and-WiFi-Coexistence) I’m just wondering if the best thing to do is delete and then re-add my ZigBee devices or if there is a better way to get them to work.
The “Device Health” feature is not the most robust part of SmartThings. Many users have perfectly fine devices that are reported as “Unavailable” even though they are absolutely fine. You can just disable the “Device Health” feature in your phone’s ST App.
I would not recommend removing the Cree Connected Bulbs from SmartThings as it can be a pain to get them to re-pair with the hub.
Thanks for the reply. I forgot to mention in my original post that I have disabled the “Device Health” feature in the app and they are still showing as “Unavailable”. And when I go to my device list in the Web IDE I see those devices listed as “OFFLINE”. It’s just strange that I can still control them and they were working for over a month with no problems and now all of a sudden I’m having these issues. I wonder what caused it.
The “Device offline” problem is an ongoing issue with SmartThings and has affected many customers with many different types of devices. It’s unclear exactly what is causing the issue, but quite a few people have seen exactly the same thing that you are seeing: the device can still be controlled from the app, but it is marked as off-line or unavailable.
The best thing to do is to contact support as there may be some things they can see from their side. It’s certainly annoying, and I’m sorry I don’t know of any workarounds to offer you. It’s just something that’s been happening for the last few months with the platform. It doesn’t seem to be specific to any particular device, or even a particular protocol. 
I should also say that it’s certainly true that there can be issues with Wi-Fi drowning out zigbee, but that’s not usually the problem that fits the symptoms you’re describing. In those cases, you wouldn’t be able to control the device from the app either.
So the strangest thing happened, I just checked my SmartThings app and the problem has gone away. All my devices are back to being online including the ZigBee light bulbs. I didn’t really do anything so I have no idea why they are working all of a sudden. Oh well, hopefully this doesn’t happen again any time soon.
The “device off-line” notation is made by your cloud account, not by your local hub. So the problem is that people have been seeing may have to do with the cloud account syncing with the hub, which may also explain why it just seems to mysteriously fix itself from time to time. 
Definitely report it to support if it happens again, the more reports they get with specific dates, times, and devices, the better they will be able to track down the cause for everyone.
it’s unreliable as can be
i’ve got a ecosmart bulb (from Home Depot) that uses the Zigbee Dimmer device handler… it gets reported as offline quite often, even though it still works… though sometimes, it’s actually offline… super unreliable
I have GP-U999SJVLBAA Magnetic Motion Sensor and do have the same issue. Some of my sensors became unavailable, however they do not want to repair themselves. There is some flaw in the firmware/communication protocol.