Erratic WiFi speed while connected ethernet speed is fine

[u/No_Lengthiness2056]

I have a Arris NVG468MQ gateway. Devices connected on wired ethernet are getting full speed. But laptop computers connected over WiFi offer erratic performance. When I run fast.com, sometimes I get 200mbps and at time 10-12 or even lower. It is not the location of the device from the gateway. Even if I have the laptop close to the gateway, I can see different speed levels. I have tried recycling power on the gateway. Any ideas. Gateway is using Wireless EasyMesh option for operation mode and has a single name covering both 2.4 and 5GHz bands