@gfw Can now confirm: Restarting the router and the devices with separate 2.4GHz and 5GHz SSIDs temporarily gives all devices access to the network. Changing settings makes no difference. I refuse to...

@Tony Thanks for the reply. Separating 2.4GHz and 5GHz SSIDs has made no difference, but I'll try changing some other details and see if anything helps.

I have a smart thermostat, a wireless printer, and a mixed bag of Windows laptops, Android phones and Raspberry Pis. 2.4GHz and 5GHz wifi are running, on the same SSID and password. One of the...