Oh, I'm an idiot. For some reason I had it in my head that setting the PVID for the IOT ports would add the VLAN tag to their traffic, thus "tagging" them and so the VLAN membership was, well......

So, it is definately the switch and not anything going on with the Deco. I moved one of the switches to hang directly off an edge router port configued just like the Deco... trunk VLAN 1 and...

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...