When it disconnects, go to Diagnostic and check if there is any error in test result. Provide a screenshot pls. Is it a brand new router? You may try to get a replacement to see it will be solved.

LAN ports of your router are gigabit ports? Can you provide brand and model number of it?

Login web interface of WPA4220 by running its utility. Change its default SSID and password. Try to reconnect your iphone.

my ISP has registered the MAC address of this device and will not allow me to change it... I don't understand why your ISP cannot help to change it after you use a new device... On status page of...

What is the problem indeed? Can you describe it in details?

If we connect more than 15 devices, maybe they can do nothing although they are connected or the connection may be quite unstable... It cannot be improved by modifying settings on the router. I...