I’m sure that’s very frustrating. A lot of people report the same issues on the smartthings platform, as you can see from the forum, so I don’t think there’s one answer. It’s just a fairly fragile implementation.
( that’s not due to the third-party standards being used, either zwave or Zigbee: both have proven to be very reliable in other systems. Ring uses zwave for their security system; Philips uses Zigbee for hue lighting. Both easily achieve a maintenance free operating period (MFOP) of six months or more for most customers not using smartthings. )
So… There are some things you can do to help improve the situation when you are using smartthings, but it’s just a step-by-step, device by device check of multiple factors that might improve reliability somewhat. If you want to start going into those, we can, but the base issue is the platform. Smartthings is a very powerful, very versatile system with a nice app. But reliability is not a competitive advantage for it.
OK, the first thing is to know which protocols you are using for each device, since smartthings is a multi protocol platform.
Your topic title said “zwave“ but the Sengled devices are all Zigbee or WiFi. Since zwave repeats only for Z wave and zigbee repeat only for zigbee, the protocol does make a difference in terms of “strengthening the mesh,“ improving the quality of the local networks you have to pass messages around.
So if you want to start digging into various individual issues, we’d need to know the answers to the following questions in order to help:
what country are you in?
what’s the model number of your smartthings hub? (It should be on a label on the bottom of the unit)
what’s the specific brand and model number of a device that is giving you trouble?
Once we have that information, we can start suggesting individual troubleshooting steps for that device. But they might be different for a different device, it all comes back to the first rule of home automation: “the model number matters.“
I know this seems like a lot of work that shouldn’t be necessary, and I understand completely if you don’t want to do any of it. I’m just another customer, and I myself changed all of my critical use cases over to a different platform (in my case, Apple’s HomeKit) A few years ago because I realized reliability was at the top of my own priorities for Home Automation. (I use a wheelchair and have limited use of my hands, so I really need a long MFOP, at least six months and preferably a year.) But smartthings does have some advanced features that I find useful for some convenience use cases, so I still run it in addition to my primary system.
So just let us know what you’d like to do next. I know it’s really frustrating.