Iris ZigBee sensors (wet, motion and contact) are all become unavailable for hours, sometimes for days, sometimes getting available again, and sometimes remain unavailable until reset.
I always assumed Hue bulbs will blindly transmit ZigBee signal, and if that’s the case, I have plenty of network coverage.
I found some similar topics, without decisive solutions, so I wonder which support I should call? ST? Iris?
What do you mean by “unavailable”?
If you are referring to the indication in the SmartThings App, then just disable “Device Health”. On average, it causes more trouble than it can possibly resolve.
Beware that the disabled setting is sometimes reset to “enabled” without warning.
Thanks for the reply, Terry (BTW, Action Tiles rules!)
Unfortunately, not only they are shown as unavailable by the Device Health, they don’t report state change as well (e.g. open/closed). Also, I think the Device Health was fixed some time ago and reliably shows availability by now.
Hue bulbs are their own, separate mesh from SmartThings. Do you have any other mains powered zigbee devices?
For non-SmartThings branded sensors, I doubt you will get Support from SmartThings.
I use PEQ branded sensors (also manufactured by CentraLite) without any problems.
Unless your Hub is borked, the most likely issue is ZigBee mesh / RF interference or range.
100s of topics and recommendations on this.
My hue is in my mesh and act as a repeater but I don’t use their hub.
Hue bulbs are their own, separate mesh from SmartThings.
I know they require their own hub, but I was pretty sure they are part of a normal Zigbee mesh. Do you know how we can check?
Do you have any other mains powered zigbee devices?
No, only Hue. I think I’ll try to plug in a powered switch in the middle of the room, just to test it out.
100s of topics and recommendations on this.
They were easy to find. I usually follow the solutions I find before posting.
Re switching to Z-Wave, I’d hate to do that. I find Iris sensors family a perfect price/form-factor/functionality combo.
Well… Good, thanks; but then, with 100s of existing solutions, you’re in a rough spot if nothing works.
One possibility:
As with any problem, isolation is key. I would recommend removing the Iris sensors, one-by-one (or all of them and add them back one-by-one). If you add any powered outlets (repeaters), then perform the Mesh Heal process.
If you’re using the hue bridge, SmartThings communicates to hue devices via LAN. Totally Separate zigbee mesh.
Definitely! … But there’s a chance they are on the same ZigBee Channel and causing interference.
Be sure to check your SmartThings Hub ZigBee Channel (under Hub in https://account.SmartThings.com) as well as in the Hue App under Bridge settings (if you’re using the Bridge).
As noted - Hue bulbs attached to a Hue bridge don’t repeat/support other non-Hue Zigbee devices. They are not a part of the “normal” (I assume you mean ZHA) Zigbee mesh that the SmartThings hub creates, so Hue ZLL lights/bridge won’t help your SmartThings ZHA Zigbee devices.
Hue bridge is ZLL, SmartThings hub is ZHA.
What really helps folks help you is if you summarize what you’ve tried when you ask for assistance, that way you don’t get redundant info - that wastes everyone’s time. 
The communication between the hubs is not the same as devices mesh. From what I know, the bulbs retranslate ZigBee signal regardless of if it is their own or just a general ZigBee mesh.
Whomever told you that gave you really bad information. Line-powered Zigbee devices which as repeaters only can repeat messages to nodes which are included on the network. They do not act as simple radio relays that retransmit what they receive. Your Hue bulbs, if connected to the bridge are not part of the ST Zigbee mesh and are therefore invisible to the SmartThings Zigbee network.
Got it. I’ll try ro plug in something line-powered and will report back.
If you have any Iris or SmartThings SmartPlugs, those are your top two choices. The key to remember is that they must be included into the Zigbee mesh. You do that by following the normal SmartThings device installation process.
Once a line-powered Zigbee device has been included, SmartThings knows it exists, how to reach it through other nodes (if applicable) and that the device has routing capability. The new node also has an awareness of it’s neighbors and can direct messages to them as needed. Zigbee allows for up to 12 hops from the hub to the end device so the more line-powered device you add, the stronger your mesh gets.
I have no doubt that a couple strategically placed SmartPlugs will address your issue. I have 46 of them, there are no dead spots in my mesh! 
I strategically placed 2 Iris Smart Plugs as suggested, and all sensors easily reconnected. I hope it will stick! Will report in a week!
Thanks everybody for the useful advice!
I think you’re well on your way to having a stable mesh. Please do report back with how your system performs. You might have to do a Zigbee heal to ensure that all of your devices see the new repeaters. To do this you only need to power down the SmartThings hub for about 15-20 minutes. This will cause devices to seek out new neighbors in an attempt to communicate with the coordinator (hub). If you experience any devices dropping off now, please make that your next troubleshooting step.
Thanks, @SteveWhite! After 4 days of having the plugs, all the sensors are still online! I am a bit bummed to have to maintain 2 networks, but for some reason all the nice plugged things (outlets, switches, dimmers) are z-wave and all the nice small things (sensors) are ZigBee.
In any way, thanks for pointing that I can’t rely on Hue for the ZigBee mesh!