I have it with my SY SmartSense Motion detectors (2015) version. I also have it with one particular WeMo switch. Strange it is just this one switch.
Was wiring to some new switches yesterday and had to turn power off. Upon power restore, I had 2 switches that reported “Unavailable”. Turned off the feature, tested the 2 switches and they worked as they should have. Turned the feature back on and all has been well since.
Something is the new feature is broke.
I just had about 10 divices slowly go to "unavailable"mode. All are in-wall switches (no battery required) This started right at 7pm. I found this post and deactivated the Device Health in the Smartthings app. As soon as I did all of my devices came back online. This appears to be the best solution.
The problem with that theory is even after I turned off the Health app and it said on;one the device was unavailable still. In your case I assume Z-Wave in my case WeMo. I only have four WeMo left and slowly switching over to GE Z-Wave.
Yes, sorry mine are z-wave only. I was just surprised at how quickly everything was restored once Device Health was disabled. Good luck. I know how frustrating it can be when something goes offline and appears unfixable at the time.
Same here, I have around 20 Z-wave switches. Half of them became unavailable yesterday, and routines did work last night. I just turned off the HEALTH check and everything seems normal now.
This is exactly what happened to me, down to the minute. With Device Health on, only about 50% of the switches show available, others are not. Turning off, they work fine.
I had four devices do this in the lase few days. Three of them are Z-Wave and the fourth is ST Zigbee. In all four cases I went to the device and pushed the local button and the device operated the load normally. A few seconds later the device became available on my ST app.
I’ve no clue what happened but odd things happening on my network aren’t unusual. About once a month a device will just stop working. I go to it and use the replace function to replace it with itself and every thing is fine after that.
I’ve about 40 devices on my network. Mostly it’s fine but I don’t want my life-support controlled by it.
I just took a few minutes after work and did this (turn them on and off manually at the switch) and they finally cleared up on My Things list with Device Health turned on. What a PITA. All Z-Wave dimmers and one switch for me.
so if turning device health off doesn’t work then the workaround is to remove and readd the device or just clicking reset on the device is enough?
luckily I only show two devices but I can see how this would get annoying real quick for a larger count of offline devices that need the workaround plus some devices are placed on the ceiling…time to get the ladder …sigh
kinda odd that ‘device health’ broke things, maybe should be called ‘device coma’
There are now about six threads with similar reports. Very frustrating. 
Definitely report it to support if you haven’t already. They may be able to see something from their side.
It might be related to the following
I just started to notice this problem on a FortrezZ MIMOlite unit in the past few days. Google brought me to this thread. Upon disabling Device Health the MIMOlite was immediately back within control.
This has strange implications for the Device Health system… what’s it actually for since, you know, the indicator isn’t actually right?
I also have a Smartthings Multi Purpose sensor that went off line about April 1, 2017. In my case I think it was triggered by a power outage at my house. This device is in a back garage which is quite a distance from the hub. It relies on a smart plug which is located in between to provide mesh network connectivity to the hub. When the power went out it lost the mesh network.
The thing I don’t understand is that when the power came back on why didn’t it automatically reconnect. I took the battery out as suggested above and then it was fine. Thanks for that tip.
I’m not sure what might have changed but I haven’t had a device go unavailable for about a week now. SmartThings folks, any news on this issue? Was the problem identified and corrected or have I just been lucky?
I have had this for a while and can confirm that the device health feature was causing it. I’m going to stick with Check All Devices and Simple Device Viewer App. Might want to mark this as solved as that feature is no working.
I continued to have issues with one of my door sensors going unavailable. Been having this issue for several weeks, every since replacing its original battery. Turning off the device health feature seems to just hide the problem. The device would no longer say “unavailable” but never was active. So I turned the health feature back on, because it was nice to know that the device is actually not working as it should.
I was able to fix my problem. I noticed if I pushed in on the battery, the sensor would work. Not sure if the battery I’m using (Energizer brand CR2450) is slightly thinner than the original battery they came shipped with and not making full contact. But I had to fold up and wedge a small piece of paper on top of the battery and tape the cover on to keep the battery in contact. Now it works!
It would be nice to know if SmartThings recommends a certain brand battery. I forget the original they came shipped with as I replaced the batteries on all my sensors. And it’s weird that the problem only exists on one of the four sensors.
You might want to check out this thread…
As this issue is still continuing, I replied to a comment on reddit regarding this very same issue. I discussed the battery reset procedure and when I performed it, the batteries had been completely drained. Here is the reply directly from an ST dev:
Take the battery readings with a grain of salt. We are continuing to work with the device manufacturers (in this case, probably Centralite) to see what we can do to improve battery reporting.
The battery curve of these Li-Ion coin cells (and not everyone uses the same ones) makes it non-trivial to provide great percentage reporting even if we could measure the voltage (and voltage under load) accurately.
I know this doesn’t address your specific issue exactly, but I felt it was good information for this forum.
I have a multi-sensor that has been unavailable for the last two weeks. Does anyone know how to get it back online. This happened with my first multi sensor so I decided to change it. the new one worked for three days then back to unavailable
Sometimes just removing the battery and reinserting it after a few seconds works. However, holding down the reset button while reinserting the battery has worked for me most often. Let go of the reset button as soon as you see the amber light. Go to Things -> Add A Thing and your device should blink green or blue (forgot which color). Go back to the device and it should be back online. This has worked for me numerous times.