I have a Smart Hub 2 and a single wi fi disc . Disc and hub are on ground floor of our house and it generally shows connection between the 2 as very good.
However I often try to connect to internet from phone or tablet from upstairs and against the wi fi icon it shows an exclamation mark which I believe means wi fi but no internet connection. I usually get over this by disconnecting from wi fi and then reconnecting.
Eventually this was getting too regular so tried to reposition disc but with same results. Eventually I plugged disc in to an Ethernet connection which was conviniently near the disc. Since I have tried that I have had no further issues of being unable to access internet and have never seen the exclamation mark with my wi fi symbol. Happy to leave it like this but wondered if anyone else has had a similar issue.
Also on BT app it now always shows an excellent connection between disc and hub which I assume is because it is using Ethernet and not wi fi.