2.4 Ghz network issue

Your gateway can support up to five Wi-Fi network configurations.  You can use a mixture in your home.  Did you keep the default network that was installed on the gateway?  It is 2.4 GHz + 5 GHz with WPA2/WPA3 security.  It should work for most devices.  2.4 GHz with reduced security of WPA/WPA2 should be reserved for devices that don't like the default network. Perhaps your devices are requiring the higher level of security (WPA2/WPA3). Typical devices that work better on the dedicated 2.4 GHz WPA/WPA2 network include older printers and some home security cameras and garage door openers and the like.  Because it is lower security, use it as little as possible and make the network hidden.   Oh, is it possible that you did make your 2.4 GHz network hidden?  As I recall, it's a slider at the very bottom of the settings.  You can make it not hidden until you get everything set up, then make it hidden later.

@Richard L the comments from @nc1037 are spot on. 

If you have not done so, make the SSID name unique, like - Printer (completely different than your regular home SSID name. Then reboot the gateway and your devices. Sometimes, the cache on the device populates the log-in screen with old data. 

Let us know what works. 

Thanks for your suggestions.

I am using an unique SSID for the 2.4GHz band and its not hidden.

I have an old Brother printer and Philips WIZ app which only work on 2.4 GHz band and now I cannot use them because they will not see the network.

Rebooted the gateway and reset the WIZ app.

Didn't help.

If WPA/WPA2 didn’t work, perhaps WPA2 (only) will work.