VLAN fails for IOT devices
So, I just got done adding some TP-Link items to my network in order to get better WiFi coverage while also segregating IOT devices into a VLAN. Everything works, sort of.
I have an edge router splitting my network off into a DMZ, Guest, and LAN networks. On the LAN network, I have a deco m5 acting as a router and behind it I split off into two other backhauled m5s and a couple managed switches. The Deco has Guest WiFi turned on and the VLAN id set to 10. Yes, double NAT but has worked before with a different router where the m5 is now. Also, I'm using the Guest WiFi for my IOT devices. Actual guests connect to a different AP that's on a different VLAN coming directly off the edge router.
Anyway, everything connected to the IOT (Deco Guest) WiFi works just fine. Harmony Hub, Honeywell Thermostats, Alexa devices, etc. But, I've got a couple IOT devices I'm trying to hard-wire either because they need to be (SmartThings v2 hub, Hue Hub) or I want them to be (networked receiver, smart TV). To accomplish this, I have two TL-SG105E switches sitting on the same wire as the backhauled m5s. A simple diagram with the relevant parts looks something like the image below.
In the switch pictured above, I've got the VLAN setup as follows.
Any device connected to ports 1-3 work as you would expect. When I connect a laptop (Windows 10) to ports 4 or 5, it also works. Shows up in the Deco app as in the Guest Network with a wired connection. IP config on Windows shows everything happy as a clam. Any IOT device however, failes miserably. Best guess from what I'm seeing is that they don't actually get a proper DHCP response. Deco doesn't even recognize it's on the network. On my smart tv (Android) I tried setting the IP manually using a free IP with /24 network size, set gateway to the main m5 router, set DNS, etc. But even that didn't work.
There isn't anything I can change (that I'm aware of) on the Deco. Only thing I can think is I'm doing something blindingly dumb on the switch that's causing traffic not to route to the IOT devices while Windows has something in their TCP/IP stack that can deal with it.
Can someone tell me what to check or try before I pull what's left of my hair out?