Although the Whole Home WiFi is generally working well around our three story house, I have experienced a few random dropouts of connected devices. Looking at local wifi transmissions with WiFi Analyzer on a laptop I was surprised to find that all four neighbouring wifi routers were on channel 11 and guess what? The Home Hub WiFi was on channel 11 too! All transmissions were with a reasonably strong signal so it's hardly surprising that there's interference.
I thought that the point of the Whole Home WiFi was to find a quiet channel. Having exchanged email with BT support it turns out that the master disc only searches for a channel with the fewest SSIDs upon start up. If there is no re-boot for days or months then competing transmissions are not detected and avoided. This is disappointing. BT said that this was no different to most other systems with the exception of BT's Home Hubs. But the Whole Home WiFi is supposed to improve over other systems. Unfortunately I am with Plusnet and the Home Hub is not yet available. In any case it would probably not have the range of the Whole Home WiFi which certainly is effective at distributing a strong signal all around the house.
After monitoring the situation for a couple of weeks and seeing no change, suddenly the neighbouring transmissions have all moved to other 2.4GHz channels so the problem (and the dropouts) have gone away for the time being. It will be interesting to see if future dropouts are fixed by a re-boot. Hopefully future firmware updates will fix this shortcoming.