WiFi is subject to not only interference but devices that hog the airspace. The only known fixes are widely discussed such as moving closer to the router or WAP and moving to a system where you are the ONLY connection on the less crowded 5GHz WiFi.

Repeaters tend to cause more issues than solve such.

There's another issue is that ping times only stay (nearly) the same under lab conditions. I've shown this many times over the years but many new to networking seem unsettled by how ping times vary when we ping (a) over WiFi and to Internet locations.