Low Internet Performance

For the past 5 to 6 months, the WiFiservice has been blundering, not booming.

I log into YouTube on the TV and I get a screen of gray boxes instead of the video thumbnails. I'll watch a video and when I go back to the YouTube Home page, I get gray boxes again. 

I'll be watching a movie on the TV and I'll get a message saying that the WiFi has disconnected. I have to wait for a reconnection. 

Or I'll be recording a podcast and I get a message from the podcast platform that says that low frame rate has been detected.

I've used the Xfinity app to test the speed of the Gateway (last time I tested was 10 minutes ago) and the result is good. I'll restart the Gateway or the Google Cast if I have no response from the TV. 

I only have about five devices connected (a cell phone and smarta watch, a TV that uses Google Cast, a Google Nest, and a laptop.

The biggest frustration for me is that this is a daily occurance. I used to not have this problem. I live in a less than 500 sq ft studio and all of my devices are near the Gateway.

Is there anything else I can do to eliminate this problem? Thanks.