100% zwave plus here. Many issues as welll. Devices randomly stop responding. The paths are nonsensical (when a device is 5ft direct line of sight to the hub, no one is going to convince me that a sane routing algorithm with instead choose to take 3 hops that go, in total, 350ft through drywall, insulation, plywood, etc. there’s just no way that is efficient. Anyway, what I’ve noticed is clicking the Refresh button on the zwave settings page fixes the device near instantly. I am sure the Hubitat team will say this is a bad idea, but I am considering writing an app that will Refresh each device nightly. Bad idea or not, the hub’s built in zwave system doesn’t work for me so either I take matters into my own hands or I give up. It’s just super unreliable. If wifi were this unreliable it would die.
As a long time member of this forum (2 years), I have seen many posts from users who are frustrated with zwave reliability. Some users post frustration with zigbee and wifi, but zwave seems to garner the majority of posts from users who are experiencing issues. It is also clear, from many posts that many users never have a problem with zwave and its 99+ percent reliable. For myself, my zwave devices have been as reliable as my lutron devices (99+%).
I tend to believe all users and their posts, when people say they are having problems, I believe them. Also when people say their mesh has been 99+% reliable, I also believe them. At this point, I would really like to see some scientific studies on building construction materials used in homes and issues with radio protocols used by HA (zwave, zigbee, wifi, lutron). I would not be surprised to learn there are some consistences with the building materials used in homes that struggle with the zwave protocol. Maybe, foil backed drywall will typically cause a zwave mesh to be unstable and then if you live in such a home you need to choose a different protocol.
Considering the many millions of users of these various protocols worldwide, you would have thought this research would have already been done, as opposed to people making their best educated guess.
Interesting.. Can you elaborate on what it's fixing? .. Routes/responsiveness/etc?
Nothing really bad about this.. It just makes the SDK go back and re-query the node's NIF..
Lath and plaster. I feel your pain.
Actually a faraday cage would probably improve your mesh as the outside interference would be blocked. 
In any case as OP's home has foil in the ceiling only no faraday cage is created and there should be little if at all impact on z wave (or any other EM) signal strength through the rest of the home.
...as long as the home is only single-storey
You would think that would be the case but it's not. It's true that the inside walls are not foil but the foil on the ceiling appears to stop the signal from radiating very far. Additionally, the house is brick and stucco with 2x6 framing and it's a walk-out. So, half of the first/lower floor is underground. It's also a weird "U" shape with two long legs on each end. The best part is that it was built in 1998 and everything was finish drywalled! So, running cable has been an absolute blast. But at least I have wired wall-mount phone jacks in every bathroom by the toilet!!! They thought of that!
What's a good way to find out more about local WiFi?
Most TP-Link Kasa devices support local WiFi and there is an excellent community module created by djgutheinz that works great. You can block cloud access in your router to prevent them from calling home at all if you want. I also believe the Lutron Caseta devices stay local. I'm not sure what else is local. My Leviton devices seem to be cloud only for now unless somebody creates a local module for them. I was very surprised how quickly the Kasa devices respond. Absolutely instantaneous even through the Homebridge plugin I'm using with my iPhone.
He's also got a toggle switch to disconnect from the Kasa Cloud right in the driver for each device. Pretty sweet.
I'm no signal engineer, but I would have thought that ceiling absorption would reduce propagation but not more than walls. I suppose it's also possible that reflected signals from the foil could interfere with transmission somewhat.
Sure. So say I turn a device on via the device page. Nothing happens. I go and click Refresh for that device. Sometimes the device then responds, other times if I send the command again it responds. I note that the route then looks different, often times direct to the hub instead of having hops. The routes get worse over time it seems. Most start out direct but then slowly add more hops over time. Clicking refresh seems to fix it.
Ok, a bit off the wall here, but maybe connect an antenna on a WiFi access point to the drywall foil, so using the foil as a radiator. Yeah, complete mismatch but it may get better results any way...
His wifi is solid, it's the Z-Wave mesh that needs work.
For me - large 1720's built home I have loads of RF problems as walls are about 1.5m thick and solid, ceilings half that. Wifi, Z-Wave and ZigBee have always been problematic.
So I decided I needed to address Wifi and have done so. Great coverage now with 4 AP's Hence I have opted for WiFi wherever possible, and wired as an even better option. I have over 300 IP devices , mostly wired.
The main disadvantage is the power consumption on wireless sensors so I do use some ZigBee which works better (surprisingly) than Z-Wave. Z-Wave is just awful here. I particularly dislike the mesh aspects of both as this seems to give varying results day by day and is hard to diagnose.
So for me wired IP based supplemented with WiFi is my preference. Investigating 6LoWPAN / Thread
Bandwidth is so much better on WiFi
For a "normal" 5200 sq ft home that would be way overkill for access points (even if they just did 5ghz). I understand the "foil backed drywall" issue but... I wonder if you had invested in your Z-Wave infrastructure as aggressively as you did your WiFi network infrastructure if you would have had the issues that you have experienced.
My home is 2700 sq ft, and I have 4 UniFi access points. They provide excellent coverage! I dial down the power levels so devices will hop to the various access points as we move throughout the house. They also provide a nice level of redundancy, should one of then need to be taken offline for maintenance or a hardware failure. It is nice having a very resilient WiFi network at home.
The Ubiquity site makes it hard to figure out which components you actually need... is there an overview that's relatively easily digestible?
My house is around the same - I have a Ubiquiti WiFi 6 LR and a Wifi 6 Lite AP.. so far so good. I wanted to get the "regular" WiFi6 AP but a lot of Ubiquiti's stuff has been out of stock for a while. I am also installing 2 LR APs at my uncle's new build house which is 5800 sq ft along with a UDM Pro. Figure I can always add some other APs as needed..
