I noticed that no devices were connected via wifi. No phones or printer.
I restarted the router. No change.I factory reset the router, some devices have connected.
One device won't connect, but I can connect it to other wifi networks. Which indicates strongly that the problem is with the router.I've tried different channels, and checked every setting.I have a Super Hub.
You could try setting up a Guest wifi network and see if the device connects to it ?
It may be a security setting on the device that is causing the problem with the main Wifi connection, e.g. WPA, WEP etc.