Thanks for the original poster of this thread it helped me find the same problem with my setup. I'm on a Smarthub 2 with FTTP connection. I had Sonos and Canon printers not appearing on my network when searching from devices on the 5ghz wifi. But the Sono's still played internet radio fine via their preprogrammed alarms, so I knew they were connected OK.
I've since set up a second wifi router cabled directly to the Smart Hub2 and running a separate 2.4ghz wifi SSID and connected the Sonos speakers to that and it's all working OK. I can now use the Sonos controller on my phone or laptop via the 5ghz BT Smarthub wifi.
I complained to BT about this via Twitter earlier this week, someone ended up ringing me and actually admitting that this is now a known issue they are looking into and that someone from their technical team would get back to me.
I asked them to update this thread and the other one with similar issues, but they haven't. So I hope this helps.
If you have time I'd recommend contacting BT and letting them know this is an issue so there's more pressure to fix it.
Add me to the list of affected users. I created this thread before realising it appears to be a widespreadh problem
My router is saying it has updated the firmware today (4th May 2021). But the version number is still set as v0.26.03.01286-BT . I've not tried to see if the issue has been fixed yet.
The last updated version to possibly correct the problem re 5GHz and 2.4GHz Bands on a FTTC router was. v0.26.04.04227-BT pushed out to some customers earlier.
If a reboot of the BT Smart Hub 2 router does not show this version or a later version then possibly the router has not yet received it.
I'm now running v0.26.04.04227-BT once the hub has been restarted it seems to have solved the issue.
I am currently running v0.26.04.04227-BT and ever since this was loaded I have been having issues especially with my Ring Camera, smart plug switches and my 2 Echo devices (Dot, Echo Show 😎
Ring Camera will not show live view - recorded activity will play
Smart Plugs do not respond to Alexa, as soon as you ask her to switch them on/off she reports they are offline yet in their own app on my phone they will respond but slower than before.
The Echos will not communicate with each other either as announcements or drop in.
The Echo show will flash the orange bar occasionally indicating network issues.
Placing the echo show in the DMZ did make things work to around 80% but that affected other things like streaming on Sky Q and Facetime calls.
I moved to the SH2 to resolve issues with the Sky Q affecting my hh4 so was initially pleased, now it seems my wifi is not stable.
BT Please Sort This!