This is an addendum to an old ticket which can be seen here:
The problem described in the old ticket is still occurring. Random devices will pull a 192.168.0.X address. I put in a new Unifi network (With a new Sonicwall) but the exact same thing is happening. The DNS server changes as well. The DNS server on the firewall is listed as 220.127.116.11, which is exactly what devices that pick up the CORRECT 192.168.1.X subnet read. However, those that get the wrong 192.168.0.X subnet read the DNS server as 18.104.22.168, which is the old TW/Spectrum DNS. I have no idea how it's grabbing this.
This "wrong subnet" problem only appears to occur with the wireless devices, as no hardwired device has shown this error so far. That leads me to believe it's either a setting in the Unifi setup (For which I've kept all of the defaults) or the way the Unifi is talking to the Sonicwall. To combat this problem with laptops I've gone in and set static IP addresses from the PC side, which seems to have corrected the problem. However, with the Nest devices, this isn't an option, as there is no way to manually enter network info.
Instead, I created a static IP for the Nest devices on the firewall. If I reboot the devices they SOMETIMES pick up on the correct subnet, and when they do, it's the static IP I gave them in the firewall. However, after a few days of working properly they suddenly drop off and pick up the wrong subnet again.
There is clearly something going on here. Looking at the devices connected through the Unifi system I can see one Nest device currently picking up a 192.168.0.3. Not only is this wrong, it's not even accurate, because if I run an Advanced IP scan I pick up about 6 or 7 more devices trying to work off of the 192.168.0.X subnet.
It's almost as if there is something else acting as a DHCP server. The DHCP server should be the firewall and nothing more. There is no Windows domain here. It's a Sonicwall, a Unifi Wireless network, and local computers.
Any suggestions would be greatly appreciated, as I am at a loss as to how these devices are getting this setup.