There are a lot of different ways to handle the possibility of interference. Many zigbee devices do channel hopping where they will adjust the frequency to find the least crowded channel. SmartThings does not do this.
Based on recent reports, it also looks like there may be QOS issues when zigbee bulbs are paired directly to the SmartThings hub rather than through the hue bridge. SmartThings may think the bulbs are ZHA repeaters And the bulbs may be dropping messages. Various different reports about this over the last 15 months, but several people have posted that removing all their zigbee bulbs from their direct connection to the hub solved a lot of zigbee network problems for them. That would be unfortunate if true, but at least it would explain why some people have such awful problems and other people don’t have any.
You can always blame wifi
But then again, it could just be local Wi-Fi interference. I’ve mentioned before that I have two provable instances of Wi-Fi interference at my house. In one case I have a Wi-Fi booster. If I put it on one wall in a room, it kills connection to all the SmartThings zigbee devices that are west of it. If I move it 90° to a different wall in the same room, everything runs fine.
And in another case, on weekdays around 330 my SmartThings arrival sensor goes bananas and keeps losing contact to the hub. In that case I suspect that one of my neighbors has boosted Wi-Fi and a kid who gets home from school around that time.
Does success require limiting approved devices?
It’s always true that in the US in a home automation set up zigbee is somewhat more fragile indoors than Zwave. There are a lot of ways to address that, with channel hopping being the most common, and obviously Phillips Hue is very successful even for people with very little technical background. And there are a lot of security systems which use zigbee devices with no issues after installation. But both of these recommend using a specific set of pre-approved devices.
It may be that the versatility of SmartThings and allowing for pretty much any ZHA device to be attached to the hub just opens up too many points of vulnerability. That would be sad if true, but at this point I would believe it.
@johnr @Sticks18 @erocm1231