At this point, if it was me, regardless of the stabilisation period, I factory reset the hub (at midday) tomorrow.
(others may suggest otherwise)
Clearly if the xbox can't even see the BTHomeHub3-**** SSID, but can see BTF/O, then the hub aint happy.
Try the call centre (they used to dish the hub2 out like sweets) - 0800 111 4567
They should be able to send a replacement hub3 out, plus they'll more than likely ask for the other one back