One of 3 TVs is pixelating

We have 1 hardwired box connected to a TV.  We have one TV in the same room as the WiFi/router box that is connected with an Xfinity wifi box.  We have one TV in the next room to the WiFi/router box which is connected via an Xfinit wifi box.  

Problem:

The one TV in the room next to the wifi/router pixelates.  Neither of the other two TVs experience this.  All TVs are similar LG TVs.

What is causing the pixelation and how to fix?