There are several threads concerning devices being “unavailable”. As always, you should report it to ST support.
About two weeks ago, some of my devides started going "offline" in the app, and in the developer console I see the same thing. Some of them would 'recover' when the switch was toggled. Some could even be controlled while being "offline" via Alexa voice controls that still seemed to work, although the app had lost all control of them. Still, they come and go, and I still have about 10 devices OFFLINE for now QUITE some time.
Smartthings support says they have a bug, and can't provide any guidance as to time for a fix. They say I should go and remove then add them again (Takes LONG TIME, I have 10 smart apps on each device that would need to be setup again). Support also says other people have reported the same thing...
So what gives? I can't run around the house and spend 4 hours fixing…
I like the concept of Device Health, but I continue to have false offline notifications in the mobile app for the same 2 zwave switches (using the stock ST DTH, not mine) that always work via the mobile app.
In the beginning, Device Health seemed to work just fine, but lately it's reporting more offline devices that aren't really offline. ST support hasn't been helpful, and only offer the typical "delete device and start over" answer; which I did do, but it did not help at all.
Anyone else giving up on Device Health?
So this has been happening to my osram gardenspot and outdoor jasco switch. Have a ticket into support but it has been several weeks without help.
I have removed and repaired as well as moved the hub within 10 ft of the devices. I also have a Iris plug and centralize plug and he outdoor switch to help the mesh.