With the help of Joel from the BT Helpdesk (thank you) here is the solution that worked for me.
1. Turn off all the Discs except for Disk 1 which is connected to the router.
2. Factory reset Disc1 and allow it to connect
3. Start the BT App and go through the set up process for Disc 1
4. Now add the remaining 5 disc as normal.
in short it was a complete rebuild. My problem was Discs 5 and 6 we’re not Cloning after a factory reset.