Thought it was worth sharing, in case others are experiencing the same problems I did.
I started to develop my Smart Home with camera's, sensors, lights, switches and plugs. Simple automation run primarily by the Amazon fairy (Alexa). Everything seems like I was on track ... ~150Mbps to the door and the Smart Hub was working very well.
I started running quite a lot of things from my Smart Hub 2 and boosted signal with some wi-fi extenders, for good measure, to reach the extremities of the house. All seemed to be working fine but without realising it, as I was adding more devices, the wi-fi network was becoming more unstable.
Perhaps I should have done better homework, but I've now discovered that there's a cap on how many devices can work on a wi-fi channel in a stable manner (which makes sense!) It got to a point where I was having to reboot my Smart Hub 2 every night just to maintain the network to a reasonable degree of stability. Lots of digging into the situation later and it seems that the maximum number of devices is 32 on each SSID channel, i.e. 32 devices on 2.4GHz and 32 devices on 5GHz per SSID. Most of my devices run on the 2.4GHz band (~45 devices) which was obviously, with hindsight, causing the problem. Even with extenders I was still registering all the devices back on the Smart Hub 2 DHCP and essentially the connections were being managed there.
I tried various options including a separate router running additional channels and a combination of the extenders, again. This worked fairly but it still wasn't a stable network - not enough to play Stadia at 4k anyway, or even HD properly. Speeds at the back of the house were sitting at a reasonable ~40Mbps through the 5GHz extender but not "stable". The extenders, and the new router, were also used to break out the 2.4GHz and 5GHz bands into separate SSID's.
I've now switched to a dual band Mesh wi-fi network (TP-Link Deco S4 kit - 3 units) with the primary Deco wired into the back of my Smart Hub. There are plenty of other choices, including Netgear Orbi (recommended to me by a friend but upwards of £500 for 3 units I would have needed) or the BT discs (recommended by another friend but BT want £20pcm or about £250 for the 3 units I would have needed). I now have good speed (~70-80Mbps), and a stable network accessible across my whole house. I've removed all the other kits, i.e. extra router and extenders, and turned off the Smart Hub 2 wi-fi, as they serve no purpose any more with the coverage from the Mesh network (which is also rated for up to 100 devices). The new Mesh network runs its own DHCP and manages itself as a separate network entirely. Don't know why I didn't do it sooner.
If there are other things I could have done with the Smart Hub 2, maybe let me know as well. Thanks all. Hope this is useful for others.
That's why smarter smart home kit works on the likes of Zigbee. So you only have one network connection to the router with a hub & all the smart devices talk to it & each other through their own mesh.
2 years from that post and I run a mix of WiFi, Zigbee (via Home Assistant and mostly MQTT) as well as some low power protocols for my tado system.
Also with the fibre internet connection I've now got I use a tri-band mesh network to manage the increased speeds - currently eero Pro 6 which manages the household very well.
Looking forward to having to mix things up in the near future when Matter gets into the devices properly. 😁