Ultra hub compatibility mode for 2.4ghz is a joke.

[ChrisO_SWC]

If you rely on smart devices, plugs, bulbs etc DO NOT upgrade to the ultra hub, it does not support those devices on 2.4ghz WiFi.

[Cynric]

@ChrisO_SWC  Hmmm, well I connect nearly everything (where possible) by Ethernet and PowerLine because I'm surrounded by neighbours. So I'm running out of ideas. There is a thread on the forum about alternative routers, but obviously it's an expense that shouldn't be needed. On the other hand a good one should work on any ISP.

[Amber1983]

Just an update for anyone else hitting these problems.

I got an ultrahub in October 2024 and recently tried to set up a Drayton Wiser Hub.

It was a complete pain, looking into it, in my case the Wiser hub was stuck in a DHCP loop and would never get an IP address.

As mentioned in these replies, It's now impossible to split the 2.4GHZ band away from 5GHZ, because its managed by 'Super WIFI' so the only option I had was to connect an older router with a separate SSID for 2.4GHZ, turn of its DHCP, give it an IP in the subnet range of the ultrahub, then ensure that IP is not in the DHCP range of the ultrahub. 
Hopefully this helps someone and maybe Vodafone would consider adding something to their trouble shooting information.