Its a flaky App. This may help.
Uninstall the App and reinstall the latest version. Then the first thing to be aware of is you need to be connected to your Home WiFi in order for the app to connect to the Hub. It won't allow the connection if you're on a Guest network, VPN or Mobile data. If this still doesn't help, try clearing the data within the Connect App. These steps will help you do that:
For your Apple device, if you're on iOS 15 then you can try this: Open Settings > Tap your name > Tap iCloud > Tap Manage Settings > Tap the Connect App > Tap Delete Data. If you're on iOS 16 then just delete the app from your device, restart the handset and then redownload the app.
For your Android device, you can try this: Open settings > Apps > Connect App > Storage > Clear data / Clear cache.
Or, see this other possible solution - to get this to work you have to disable the 5ghz wifi on the hub5 so the Connect app connects through 2.4ghz and then works fine.
Also make sure that you reboot the Hub after doing these and try again.
I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired, 1 WiFi, 1 on PA) Hub5 in modem mode with Apple Airport Extreme Router +2 Airport Express's. On 250Mbps, Talk Anytime Phone, x2 Mobile SIM only iPhones.