Of which two of those slaves, 1 has a Sky Q STB plugged in via ethernet cable, 1 has a Sky Q Mini STB plugged in via ethernet cable.
Back in February I was moved back to a lower sky BB router firmware version as a sky Q upgrade had knocked out my BT whole home mesh network. I plug in a sky Q STB and a mini STB in to two BT whole-home mesh discs. I arranged this via a helpful Sky engineer by moving me back from 5.14.2249.R to 5.11.1993.R. It looks like I'm now on 5.14.2390.R on the Sky BB router.
I don't know why a Sky Q upgrade needed to be addressed by rolling back broadband router firmware but it resolved the issue.
On Saturday morning I noticed the BT disks were flashing again. I have isolated the problem and it looks like again, Ethernet backhaul on my BT disks is not working because as soon as I disconnect physical cables from the BT disks, everything works again.
it's just annoying as I'm now unable to plug in the sky boxes to my BT disks and have to rely on Wi-Fi everywhere.
Whilst the Sky Q STB connects for a couple of minutes via Wifi, it then disconnects but moreover, corrupts my entire network until I go in to the Sky Q "0 0 1 Select" engineer menu to turn of 2.4Ghz and 5 Ghz wifi again (i.e. remove any internet connectivity from the Sky Q box).
It's as if as soon as I connect Sky Q to any interactive services (i.e. wirelessly to my BT whole-home managed network, or physically via an ethernet cable to this same network), it disrupts my network.
I've posted this in the Sky Q forum because it's only when I isolate my Sky Q boxes that this issue is fixed (albeit by a workaround which means I can't access Sky Q services). I know this issue has been referenced here too.