I have got several devices connected at WiFi. But each device is losing the connection and eg iphones connect to 4G. Connect again with WiFi question comes for password. Fill it with the same and sometimes you have to true with no result. After a time, without action, there is connection again. It happens to several devices in no patern. Then that device and then another. Very strange. I will try tomorrow to connect the three decos with Ethernet cable. Is possible for me. And behind nr1 deco a switch for all connections in the house and the two slaves. 
any other possible solutions?