I did do a factory reset on the black disc before connecting it to my network but not on the SH2 which is just a couple weeks out of the box. See if your mobile phone still sees the BT Wifi hot spot even when you have both wifi bands turned off on the SH2.
Dual-band AC1200 wi-fi gives you fast wi-fi as you move from room to room Three discs remove dead spots, creating a complete wi-fi network, so every device stays connected everywhere in your home These discs only work with other Mini Whole Home Wi-Fi discs