Why does my SmartThings hub disappear from the app?

The short answer

Finding new gadgets uses local discovery messages some routers block. The gadget is usually still online. What's broken is your phone's ability to see it, and that is a network setting rather than a fault with the device.

What's happening underneath

Significant for Matter and for app discovery.

Source: Manufacturer documentation

Try these, in this order

• • Plug the hub into the router with a network cable where you can.
• • Keep the same Wi-Fi name and password when you change routers — then nothing needs re-pairing.
• • Turn off 'client isolation' while adding new gadgets.
• • Check the signal where the gadget actually lives, not where you're standing.
• • Move the router off the floor and out of any cupboard before buying anything.
• • Put the gadget and your phone on the same Wi-Fi name.
• • Restart the gadget before the router — it is quicker and it fixes more.

Setting it up again properly

• • Stand next to your router while you set it up, then move the gadget to where it lives.
• • Put your phone on the 2.4 GHz network name for the setup, or use one name for both bands so the phone can follow.
• • If your router splits bands into two names, turn the 5 GHz one off for five minutes rather than fighting it.
• • Turn mobile data off on your phone during setup — some apps quietly use it and never find the gadget.

When it's worth spending money

Almost never. A £5 cable solves most SmartThings complaints.