@Pineapple-1 

A few things could be happening.  1.  You need to simply change the wireless channel of your networks.  Some devices prefer to be on higher level channels mostly iOS but i have seen it in a few android devices as well.  2.  If the SSID is cloned, meaning the same as the Router then your device could be confused as to which AP to route the traffic through. If this happens give the RE its own SSID and see if the issue corrects itself. 

@Pineapple-1 I am having the same irritating problem with two TL-WA855RE extenders in a house of a mere 1,650 square feet.