Updating the firmware on the switches has solved this for several of us, including me. I have two of three dimmers and one switch, all had the same issue until updated.
Buy a USB z-wave stick and the Homeseer Z-flash utility.
Scroll back thru this discussion or search the forums for “Leviton” or the model numbers to see success stories from updating
yes, i updated 6 or 7 (DZ6HD) to firmware 1.20 recently and all my problems went away. I contacted leviton and told them my issue with the dimmers going offline and they mailed me a zwave update dongle and a return label for when I was done. It took a few hours but Now it’s all working again and much better than before. I also learned these dimmers do have a airgap, you pull out the bottom of the dimmer bar until it clicks (about an inch or so) who knew? No more breaker breaker crap lol.
they mail you this stick (for free) 2 day speed shipping I think not sure:
they send windows drivers and the firmware update for 4 of the zwave leviton switches, the 600w 1000w and a few plug in modules. The Aeotec is compatible with mac as well but I think it’ll require a bit more legwork on your end to get them all updated. Also while I had the zwave stick I used, Zensys tools a free program to view the inner workings of my smartthings zwave network.
Matt - Thanks for your input on this. Last week, I finally got some free time and called Leviton Customer Service and I must say they were very good. I had to get transferred a couple of times to talk to the right person, but once I did, I explained the issue and they sent me an Aeotec Z-wave USB stick via 2 day FedEx along with emailed instructions on doing the update. The instructions were a bit outdated with respect to connecting the device to SmartThings (and given the number of changes in the app in the past 6 months, who can blame them). Other than a few changes from this respect everything went pretty well. The software now supports 5 device types (DZ1KD - 1000W Dimmer, DZ6HD - 600W Dimmer, DZ15S - 15A Switch, DZPA1 - Plug in Outlet, DZPD3 - Plug in Dimmer). Of these 5 device types, I had 4 of them, so I became pretty comfortable at running the updates. They do take some time to complete (I averaged about 20 mins per device), but the process is pretty simple. So far, I have had the updates in place for about 36 hours and things seem to be stable. I am going to keep the stick for another couple of days, just to make sure everything is good before I proceed, but so far I am quite happy.
I also took a look at my Z-wave Mesh Network Topology while I had the stick. Bet ween the confusing nature of the topology map and the need to convert the Hexidecimal device numbers in SmartThings to decimal in the map, it takes some time to understand what is going on, but I think I at least now have a picture. I tried to make a drawing of which devices were connected to each other, but in the end, I had lines all over the place, so I see now why they did it with a table. It is still good information to have. Since it doesn’t seem to be a priority for SmartThings to build this capability into the tool, I may eventually buy one of these Z-wave sticks, but for now I am happy with what I have.
Thanks again for the advice from everyone.
What did you use to view the topology?
I downloaded a version of the zensys tools from this location (https://groups.google.com/forum/#!topic/openhab/n1txTwcWBjo ).
Thanks! Off to nab it
Since I’ve been battling with this for some time, I wanted to share how I fixed my issues with the Leviton DZ6HD-1BZ dimmers. It kept showing up as OFFLINE in the graph API on SmartThings and couldn’t be controlled via the app or Google Home. Factory resets and removing/re-adding didn’t work
It involves upgrading the firmware and airgapping the device.
I bought an Aeotec Z-Wave USB stick and installed it as a secondary controller to my existing Z-Wave network.
I then ordered Z-flash from Homeseer. I tried the free tool from Zensys, but I couldn’t find the proper firmware files. The files I did find we’re either encrypted (in Z-Flash) or in the wrong format (via the links you can find on Google).
Total cost is under $100 for the USB stick and software, so this only makes sense if you have lots of Leviton switches and dimmers.
In Z-Flash, I enabled my USB stick and went close to the switches I wanted to update. It doesn’t see the whole network, just those it is in code proximity to. I found out that my problem dimmers were running v1.17 of the firmware, but the latest version is v1.20. Some of the switches and dimmers had v1.18, but I didn’t notice any problems, so my assumption is that the issues are related to v1.17 firmware.
I updated the firmware (you can google for step by step guides), and then rescan in ZFlash to confirm the firmware version. Please note that the firmware version only shows up under the be Raw Data section of the SmartThings graph API. The firmware version also doesn’t get updated in SmartThings after you flash an update. You would have to remove and re-add the device to see the updated version number (no need to do this since Z-Flash already let’s you know).
My problems disappeared after this… Except for one dimmer. I tried factory reset, adding/re-adding, repairing network -and it always just showed OFFLINE. Finally, I called Leviton and they suggested an “air gap” fix. Pull out the thin dimmer panel from the bottom… Keep it out for 30 seconds. Put it back in and press on/off a few times. Voila - it now shows as ONLINE!
Anyways, hope this helps someone.
Good summary. I did the same thing a year or more ago.
One thing I’m not sure you’ve got right. In secondary controller mode, I believe the list of devices is fetched from the primary controller, i.e., your hub. So distance from the stick and PC to the device to be updated should not matter.
In my case, I could never keep my Levitons online to the hub long enough to update them. I had to force exclude them from the SmartThings mesh, factory reset them, and run the stick as a primary controller.
In that mode you pair the devices with the stick, do the update, exclude from the stick’s mesh, and add back to SmartThings. Big hassle because they get removed from all automations, etc so you have to go thru and fix everything.
Thankfully I didn’t have to do that!
It’s very odd that the secondary controllers distance isn’t a factor… Not sure why all my devices weren’t showing up unless I moved around the house.
The air gap trick was something I hadn’t read before online so hopefully it helps someone else¡
Hm… maybe I’m wrong in thinking that the list comes from the primary… dunno, really.
Also in case you have any, Zooz does not recommend or support updating firmware while using a stick in secondary controller mode.
I’ve tried it. Devices get updated but have to be factory reset afterwards. When you then pair with SmartThings Hub, they’re a new device… 
Air gap (or pop breaker for devices without an air gap switch) reboots the device. Sometimes handy!
If you call Leviton product support and explain the problem to them, they will ship you an Aeotec Z-Wave USB stick free of charge to allow you perform the OTA firmware upgrade. Using that USB stick, and the OTA firmware upgrade app Leviton provides on their own web site, the process is:
I have encountered a few Leviton devices the upgrade app was unable to discover. I was always able to resolve this issue by excluding the device, resetting the device, and re-including the device to the SmartThings hub. I have also tried the “air gap fix” in a situation such as this, but my experience was it didn’t help whereas a device reset did work. Likely that just means there are several modes of failure, and if one solution does not work then try another.
I recently purchased some of the dimmers DZ6HD. Back in November. So far, I have had no issues with them. I have three of them. I don’t see anywhere in the smart things IDE how I can see what firmware they have. Is there a way I can figure out which firmware these are on and if it’s current or not?
In the SmartThings IDE listing of Devices, click on the “Display Name” for the device you are interested in. That will bring you to a page that provides a lot of details about the device. Go to the row titled “Raw Description” and you will see an entry something like this:
zw:L type:1101 mfr:001D prod:3201 model:0001 ver:1.20 zwv:4.33 lib:03
The specific item you are looking for is “ver:1.20” - which is what your Leviton switches and dimmers should be at. If you see a version below 1.20, consider doing a firmware update as has been described earlier in this discussion. Note that if an OTA upgrade has been performed on a Leviton switch previously, the older firmware version number will still remain in the device description. This is fine, and you don’t need to do anything about that. The only way to change the device description so that it reflects the correct firmware version of the device is to exclude, and then re-include, the Leviton switch from the Z-Wave network.
If you purchased these Leviton switches in November 2020 and you were sold “new stock” then likely your switches will already have firmware version 1.20. I think most “new stock” Leviton switches sold after the end of 2019 all have 1.20.
The solution to the problem is now clear: remove the Leviton switch, install a GE switch, throw the Leviton switch away, and never, ever purchase another Leviton product.
There. All done.
On to the next problem.
I like the Leviton dimmers for 3-ways. Both the smart dimmer and the matching aux have the row of LEDs to show dim level.
I also like their form factor with the small side rocker to adjust light level. That allows you to turn on the light at its lowest level by pressing the small rocker or the last used level by pressing the large rocker.
Once I got my Levitons updated they’ve been solid.