Hmm, interesting, pretty sure those discs themselves should pick up their own IP from the Hub and with that on the same subnet, but I’ve never used the black discs, only the white ones which you can configure yourself
Perhaps factory reset those black discs and re-onboard them.
192.168.10.xxx range is assigned to devices which connect to the BT EE public hotspot which is transmitted by the home hub. Its not encrypted, so sometimes devices connect to it without you being aware.
In theory the black discs should not get an IP address from that range.
So why would my laptop connect via the EE wifi and get a 192.168.10.xxx address rather than the normal wifi method. The devices that ended up with 192.168.10.xxx addresses acted as if they were connected to the wifi BUT had no or very slow internet access. This is why I felt compelled to force the ip address on them manually
Look at any saved networks, and remove any that say either BT Wi-Fi or EE Wi-Fi, that should stop the laptop connecting to those instead of your private BT Hub network.
There may also be an option to prevent it connecting to "Open networks"
Kinda bizarre how a black disc gets an IP from that range then.
EDIT: Also if poster was connected a different WIFI network, manually changing the IP address on the end device to one within the Hub's subnet wouldnt miraculously then route traffic out via the Hub would it, considering its literally connected to a different network?