There are two specific models that are known to have problems with staying connected to the network.
The first is the GE/Jasco zwave light switches that did not require a neutral. A few months after the end of the warranty. Some fairly large percentage of these, i’m guessing around 15%, but that’s purely a guess, begin having trouble staying connected to the network. This has nothing to do with smart things, you will see the same complaints on forums from other controllers. Since the switches are out of their warranty., They are technically not defective. But it’s very annoying and it only seems to happen with this brand. You have to recycle power to the circuit, not just the switch, to fix it.
The second is the GE link zigbee lightbulbs. They drop off The network even when you’re still within warranty. Again, it doesn’t matter what the controller is, the Hue bridge has the same problem with them. Tyler has said there’s a firmware problem with them which is the reason they haven’t been certified for smartthings yet. There have been similar discussions in Phillips groups.
There are lots of other people that have problems with lots of other devices, but those all seem to involve local factors, not necessarily the model itself. I haven’t noticed any particular problem with a SmartThings controller versus a controller of another brand. It’s usually just either local interference, the way the network was laid out, or bench pairing without doing a network heal afterwards.
Much discussion about all of these in the forums.