On the 2 additional discs - can you try:
1. Delete them from the app (under Disc Details > Remove Disc)
2. One at a time, connect the disc to your router with an Ethernet cable and power on (do not unplug existing Ethernet cable to the main disc)
3. Wait for the solid blue light then press the reset button. The LED will go off then back to purple. If it doesn't press the reset again after 10 seconds
4. Wait for the disc to show solid blue (after about 90 seconds). Then wait for it to flash purple (about 15 seconds after it turns solid blue). Then go back to solid blue. You can now unplug it and locate the disc, then install using "Add Another Disc"
5. Repeat for the second add-on disc.
Ha, my BT Smarthub was a total nightmare. I asked for a refund and was told by BT support that it was simply too advanced for my SkyQ box. It's been thrown in the cupboard ever since.
Anyway, I've got the same setup as you and mine acted really strangely for a day or two (only got a red light once though) and then seemed to settle down.
BUT it's only ever once decided that the furthest disc should connected via the disc in the middle of the house - that was a day of glory. Then the stupid thing then went back to connecting direct to the main disc where it can only get a 2.4GHz "poor" orange light signal.
Hi I too have this problem - a triple pack originally all good and then now adding a twin pack. Light goes red on adding fourth. I have followed sequence poseted above but still red. I also have 2 ssids slightky different rather than all the same - can anyone help please?