Successful Hub connectivity is indicated by "signal symbol" beside your devices in the App.
It can take 10-15 minutes before this shows in the App after initially connecting to the Hub. If you do not see this connection after this time, try closing out your Airthings App and reopening it.
Symbols are outlined in purple boxes below:
In the example above, 2 devices ("Bedroom" and "Sitting room") are connected to the Hub as they display the bar signal symbol, indicating they are connected to the Hub via SmartLink, as opposed to Bluetooth.
You can see one Wave Plus ("Sitting room unhubbed") is not linked to the Hub, as it still shows the Bluetooth symbol.