Had a peaceful two days with everything working. Now today, when I try to turn on one group, half don’t come on, yet lights in another group come on.
z-wave repair shows at least three z-wave devices no longer part of the mesh.
Was there some kind of update? Is there some way to fix, without having to manually remove and add devices?
Can’t keep doing this, SmartThings.
I’m sure that’s very frustrating! Do you have any Sonos devices? There’s some really weird current bug where having multiple Sonos devices can cause intermittent Z wave failures. There’s no Clear reason why that should happen, it may be associated with runaway polling. But right now the only thing support can suggest is to remove the Sonos devices and then, indeed, the Z wave devices usually start working magically again.
http://thingsthataresmart.wiki/index.php?title=Bug:_Sonos_integration_causes_network_failure
If you don’t have Sonos devices, all I know is some other people have reported the problem occasionally, but No clear pattern.
You should repeat z-wave network repairs until this clears up, leaving at least 15 minutes in between. If those same devices continue to have problems, and are actual real devices, you may have a mesh network problem, or the devices may need to be reset.
I have one z-wave dimmer that always fails to update the mesh during a repair, yet it works reliably in its single automation. I think I probably should remove the device, reset it, re-incude it, etc. But for now I’m too lazy. As long as it works, why bother.
No Sonos.
No discovered it was one of the outlets. I couldn’t even turn the light on manually. I turned it off at the switch, did a reset, and then a repair and everything is now working. It seemed to have knocked the other two devices out of the mesh.
Luckily this is one of the devices that didn’t require me prying open small, hard to open box, like the motion sensor 
I’ll remember the 15 minutes apart. I’ve done it several times in a row, but never thought about giving it time to work inbetween.
It was an outlet. I actually had to turn it off, turn it back on, and then do a reset, and then a repair and all three devices now found.
For many z-wave devices, not all, just turning off the breaker effectively resets it and it starts working again. With some, you have to do more.
@keltymd had a similar problem last week and he solved some of his problems by pulling the little tab on the switch itself instead of the breaker. I’ve always used the ‘breaker method’ but the tab idea seems a better solution…
The tab is a good idea. I’ve tried that many times. I use the breaker as a last resort.
Another thing that works, is replace (within the mobile app).
do all the tabs turn off all Zwave devices then add them back one at a time and run a repair after each one. You will get failures for all turned off devices but the one you turned back on should not give a failure. Start to the device closest to your hub and work your way away.