Hi
I had a similar set-up to you except for a Sky Q 2TB box and BT Super fast FTTC as FTTP not available in this area. I was using 2x Sky Q minis, a Smart Hub 2 router and BT Whole Home Wi-Fi 4 Discs with both 5 and 2.4GHz wifi on router off. Like you it was unstable with what I thought was interference between the Sky mesh and the BT mesh. The sky mini in our conservatory kept losing connection and seemed to be getting worse happening several times a day.
I tried what you suggested, I had to unplug all sky devices first switch on 2.4GHz wifi on BT hub and rename the SSID. I then switched only the Sky Q main box back on and set it to the new ssid BT hub 2.4 wifi and then the next closest mini box (in bedroom), this took several attempts as it switched back to the Wholehome mesh but it finally accepted the new SSID and was all working OK. I then configured the 2nd Sky Q mini in the conservatory and this worked ok too and seemed to be a stable connection.
The only issue I had was that I have bi-fold glass doors connecting the conservatory to the dining room and when shutting the door the picture would go off but opening the door would immediately fix this. I guessed it must be using the sky mesh 5GHz signal and this was too weak. I had 2 sky boosters stored away from my original set up years ago before the BT whole home and so I added a sky booster in the dining room connected this to the Bedroom mini and the conservatory mini to the booster and no more problems with losing signal with door shut.
This set-up has been rock solid for over a week and even fast forwarding recordings on the minis work perfectly, as I use to have issues with this before.
So thanks for the advice it has been a great help.
