I have the exact same issue.
A moderate size network with many different devices, and my two SML001 allways go “offline” after around 12 hours since I moved to skyconnect.
One of them is even directly connected to the skyconnect, so it’s not a distance/interference thing…
TLDR: The solution for me was to change the Zigbee channel.
Strangely, this is never one of the recommendations as a troubleshooting step and we are in fact advised against it.
A wi-fi analyser in my case showed there was not much activity around the Zigbee default channel 15 so I suspect whatever interference there was it would have been from an analog device (eg neighbour’s baby monitor or dect phone)
But since my SmartThings was working just fine on channel 20 and I decommissioned it, I had the channel free now so was worth a try.
It’s been almost a week now and had no dropouts 
Changing the Zigbee channel is not complicated at all in ZHA, but you will have to manually repair all devices. By that I mean you just have to put HA in pairing and press each device pairing button; no need to delete the device from HA, so all your settings stay the same. Even better, I paired the edge devices via the closest repeater device (wall plugs) to make sure they establish a solid connection (it’s not clear if that actually helps)
To change the Zigbee channel I simply created a ZHA local backup then modified the channel in that json file. I also added this to the configuration.yaml just to be sure. Then proceeded with the Migrate Radio step by step process using that local backup and it only took a minute.
Hope this helps
Hi!
Today I did just that… after 2 ours getting all my devices reconnected, the Hue Motion sensors still disconnect.
I guess you were really lucky. I also moved to channel 20 as it was the least impacted by other wifi signals…
Maybe try Zigbee channel 25?
In my case wifi channels looked like they wouldn’t impact Zigbee, but interference could be from analogue sources which wouldn’t show on a wifi analyser.
It’s also important to rebuild Zigbee or any mesh network starting with the repeaters (eg wall plugs) and give those a few hours to establish a solid mesh first. Then add the edge devices.
Good luck!
This didn’t last… 
It worked perfectly for two or three weeks, but a couple of days ago all my Hue motion sensors became unavailable at roughly the same time.
As before, this only impacted the Philips Hue motion sensors, all the other Zigbee devices continued to work fine.
I’ve now moved everything to channel 24 and so far had no problems.
I tried channel 25 but my SmartThings presence sensors don’t seem to support this channel.
Interestingly, my Hue sensors and some other ST sensors all migrated on their own from channel 25 to channel 24 while I was waiting for the repeaters to establish a solid mesh 
They were all flashing red to indicate that they couldn’t connect to the controller, but within a few hours they all came back online.
I did not know Zigbee devices can do that…
Have you had better results @sergio_pt ?
Hi @cipnt ,
I had great results as soon as I migrated to zigbee2mqtt with my Conbee II. 
They are working great.
That’s interesting - I believe both zigbee2mqtt and homeassistant zha are using the same underlying libraries. Are any of your parameters different? e.g. channel?
Yes… move from SkyConnect to Conbee II.
I use the zzh adapter, which is a cc2652 chip based adapter, with zigbee2mqtt. It’s worked well for me. There are many combinations of adapters and using zha or zigbee2mqtt. They are different programs- some adapters work better on zha vs zigbee2mqtt and vice versa. The skyconnect is EFR32 based and meant for zha, but is listed as “experimental” and not recommended for a stable setup in zigbee2mqtt. I’ve never tried the conbee, some say it works great, but you will find other threads on here that mention problems
Certain conbee firmware has noted compatibility problems with zigbee2mqtt- see the docs and this github issue. You will see many reporting issues with the conbee on that github issue.
I think your issues point to a larger problem with Zigbee in general. It is supposed to be a “standard”, but unlike zwave where each device is thoroughly tested by the zwave alliance prior to certification, zigbee is looser and more of a self certification. There are devices, like aqara, that don’t fully conform to zigbee standards, and have compatibility issues with other zigbee devices. Hue has done some proprietary things with their devices in the past as well.
It will be a bit of trial and error ultimately to get things working. Personally though, if you’re getting a new adapter, I would go with one of the cc2652 based adapters from the zigbee2mqtt docs I linked above over the conbee.
I have ~130 zigbee devices, mostly IKEA bulbs. I find that every few months a 5-10 of them lose their network connection. This isn’t a radio issue as they are sitting within 20cm of another identical device that doesn’t lose the connection, but I have to re-add them.
Possibly relevant: I’ve seen this with my ~130 device ZHA network where the devices are often shut off from wall switches, but not on my other ~50 device Deconz network where the devices are not shut off from wall switches. Both are using ConbeeII radios.
-David
Had the same problem with ZHA. Zigebee Coordinator SONOFF Zigbee 3.0 USB Dongle Plus-P with latest firmware.
My Sonoff SNZB-04 door/window contacts became sporadically unavailable after 12-36 hours with ZHA.
After switching to Z2M this no longer happens.(Knock on wood - switched to Z2M about 1 week ago)
I think I read that this is probably due to the reporting interval, which is fixed with the latest Z2M version. Can’t find it anymore though unfortunately.
Strange… I have four of these and they have been the most reliable zigbee devices on my ZHA network, no matter what channel or settings
Same issue here, SML001 loosing Connection. I also have a network with many Router devices. Before it was running on Z2M without any issue. And Yes I can switch back, but would give the Official Skyconnect Dongle and ZHA a go.
Same issue with ZHA here. Some devices drop out of the network.
I also have a SkyConnect dongle, so I wanted to give ZHA a go.
Z2M had no issues (ZZH dongle).
Got 110 devices, and about 60% are router devices.
I´m using the same channel as I did on Z2M.
Is it an issue with SkyConnect, ZHA, or a combination?
There is something going with ZHA - I’ve noticed that simply restarting ZHA solves a lot of glitches.
Tried… Not working 
It turned out @Hedda was right all along… at least in my case.
There are two version of the Sonoff Zigbee dongle.
The ZBDongle-E and the SkyConnect dongle I used both have the same chip which is newer and supposedly better, but it still has some bugs.
I switched to the older ZBDongle-P controller and everything worked great since.
That Zigbee guide he linked to was also very useful, but initially I didn’t read it as carefully as I should have done.
When they say that Zigbee is very sensitive to interference, they really mean it.
Some steps that turned out to have a significant impact on the Zigbee signal for me were:
Yeps, 2024 still same challenges with SML021, also with ZHA but on the Yellow.
No problems on Deconz at all. And SML022 works like a charm on ZHA+Yellow…
Weird, have tried the usual suspects, wifi separation channels/physical, different better shielded USB extension cable on the Deconz dongle that also sits in the my Yellow. When I moved from RP4+Deconz+Phoscon to Yellow, I kept my Deconz dongle and run two Zigbee networks at the moment. Wanted to see how that panned out. Also saving me from re- pairing the many different bulbs in our home…
So slowly moving from Deconz to the built in Yellow Zigbee.
So far it seems a bit weak on radio (only how I experience it, haven’t any measuring or data on it.)
(Deconz=ConbeeII)
I also have problems with ZHA and Zigbee. I am loosing devices, but also routers (!). Even the ones close to the coordinator.
I’ve added an even longer cable to the SkyConnect. And my Zigbee network is quite evenly throughout the house. Routers the furthest away (garden) is very stable) but the Aqara T1 LED strip (3-4 meters away from the Skyconnect) is loosing connection (as some battery powered devices; which are relativly close to routers).
I don’t know what to do…
I had the same devices (with less routers) when I was on Homey, and that was very stable).
This is my network:
Some time later, this is the status:
My Aqara LED strip, my aqara T1 (no neutral) and a tuya temperature, an aqara temperature and an aqara door sensor is falling out from the network.
I shut down my HA-server for 45 minutes and powered it back on the rebuild the Zigbee network. The unavailable Aqara T1 (no neutral) who was unavailable was back available, but later that day it was unavailable again.
I dont have a clue what is going on and why routers (!) are falling from the network?! What is there left to do to get a stable network?
I eventually had to switch to Z2M from ZHA due to the network just not working. I gave ZHA a lot of time and effort. Switched channels multiple times, switched hardware controllers, moved the location, anything a forum, github ticket or reddit thread would tell me. I made the brute force switch to Z2M, which wasn’t fun resetting and reconfiguring everything. But since then, I’ve had a stable zigbee experience that works. I also switched from SkyConnect to Sonoff controller along the way, but I’m not sure that made any real difference in the end.
I had started with Smartthings and that was going well until I started wanting to do more with my devices. During the pandemic my smart home became a project of mine and I have in total over 100 zwave and zigbee devices, nearly evenly split in my home. Mostly inwall smart switches, Jasco (GE Enbrighten) or Zooz, sensors, etc…
I decided to make the jump to HA for more advanced automations and Smartthings was giving me problems adding more devices. At first it all worked well, then at some point half way through 2024, the zigbee network became unstable. I had to reload the ZHA configuration daily or messages would fail to be delivered causing automations and scenes to fail.
I started with WiFi and interference scanning. Changing channels based on 10s to 100s of grabs from diagnostics on channel congestion. I was seeing up to 88% on any channel I would swich my SkyConnect controller to. I varied the distance from the router, bought a longer USB extension cable, tried nearly everything within reason.
I then bought a Sonoff controller. I kept ZHA and transferred the network to the new controller. Immediately the network diagnostics were reporting considerably lower congestion. My chosen channel and surrounding channels were now reporting 5-45%. I thought this was it and I’d be done.
Unfortunately that was not the case and even with the lower numbers, I was still losing devices and ability to deliver messages. I was ready to pull every zigbee device I had and switch to Zwave, which has never been a problem for me. The ZooZ controler, switches and other Zwave devices I have been rock solid.
I finally decided to switch to Z2M. I read about all the elegant ways to try and do it. I just ripped the bandage and did it the hard way. I disconnected every zigbee device from ZHA, removed ZHA and installed Z2M. I was already using Ring2MQTT so I had the basics ready to go.
While that process was a pain, I did it in one evening, 41 devices and a decent amount of automations, and since then my Zigbee network has been solid. I kept using the Sonoff controller, I actually moved my home assistant back to the original location and the network interference is not an issue, everything just works.
