TL;DR - I was hoping by enabling the IoT network I'd have stable connectivity as it's at 2.4Ghz. So far...not the case. Does anyone out there have same/similar experience and what have you, or can you suggest, be done ?

The attached image is my setup, a mix of ethernet from a switch off my router for work Laptops and the Deco's broadcasting 2.4Ghz & 5Ghz to all non IoT devices on "Internet" + all IoT devices on Internet_IoT. There are upwards of 70 devices attached to the network, most are running off the Deco's and many of those are IoT devices (TP-Link bulbs and switches, Google Home products, a Leviton switch and a Good Earth light fixture).

1. One of the Deco XE75's stopped functioning properly throttling bandwidth from an already bad 50 x 10 (my over the air Wireless) to 20 x 2 last week. I've now completely reset all the Deco's and rebuilt the network from scratch, not a trivial exercise.

2. Before and now again I'm having trouble with the Google Hub constantly dropping off the IoT network and reconnecting within 2-3min normally. Other devices appear to be stable but it's hard to tell as they don't have displays. The hub has been reset multiple times and is now off the IoT network where it's stable
3. The mobile app on Android is horribly slow to report device status and often reports Deco's offline for 2-3min when I know they're actually online
4. The browser portal is worse and missing many features, it stinks

PS: I's a big, old, long, farmhouse with brick and unknown substances in the walls that block signals, that's why I have 6 Deco's indoors, 3 backhauling by ethernet and the 6th, an M5 on ethernet in my garage. The network is in Access Point mode.
Blue lines = Ethernet
Green Lines = Wireless