Wifi issues with Gateway

My devices - iphone, ipad, smart devices, keep losing connection to my Gateway wifi. The device says they are connected but the connection doesn't work (such as internet access or my phone being able to control a smart device.) This happens most evenings but can happen at any time of day. Turning the wifi setting off and then on again (phone or ipad) usually fixes it. Sometimes I restart the gateway. Sometimes I switch to my backup wifi/internet. I constantly have to reconnect my smart plugs. I spoke with a rep a few weeks ago and she noticed a wrong setting or indicator in my gateway and fixed it. Things were better for a day or two and then reverted to the same issues. She had mentioned that I may need a replacement Gateway. This doesn't appear to be an internet issue (as a hardwired internet cable works fine), just the wifi. I can't figure out how to get back to chatting with a human and the Xfinity assistant is driving me a bit nuts.