I've got a BT hub 2 but needed to boost coverage so purchased 4 mini discs. Not a problem. I downloaded the WholeHomeWiFi app and was up and running in no time. So far so good with one disc connect via ethernet cable and three via wifi. Then I realised that perhaps this wasn't the best way as it effectively made the Hub 2 redundant with the 4 discs running on a standalone network. Not a problem I thought (incorrectly). Let just factory reset everything (hub and 4 disc) and start from scratch and connect the disc to the hub via the My BT app instead. This is were the problems started. The master disc was happy to pair with the ethernet cable in, but would not play with the ethernet cable out (initial blue flashing light then solid red). I've tried factory reset a number of times. Deleting and reinstalling the app. Trying WPS to pair, making sure that my phone 'forgets network', but nothing gets me past the solid red light. I've gone back to the WholeHomeWifi app as 4 disc is better than one router (though I still want 4 disc and 1 router all in the same mesh), but nothing is playing there either. Solid red lights for theany of the 3 wifi disc (master connected to router with ethernet and solid blue)
The BT Mini Whole Home Wifi system acts as an extension of your hub, not a replacement for it, so the first disc needs to be connected as you had it before ie Ethernet to the hub and the remaining discs all connect via wifi. Hopefully if you return your system to its original working set-up you should no longer have these recent issues.
Whole Home Wi-Fi is a mesh Wi-Fi system which replaces your existing network with a new seamless, interconnected network, as opposed to being a standalone Wi-Fi repeater that extends an existing Wi-Fi network. Your router will still be used to run normal routing functions (e.g. firewall, DHCP) but is not part of the Wi-Fi mesh