I had an existing Deco XE5300 network which was running perfect.  I had connectivity issues in the basement so I added a 4th unit which is the X20.  Now on occasion one of the unit randomly goes offline and reconnects again eventually.  There is also some instability on the network where devices that are close to a unit disconnect and then reconnect.  I have rebooted a rew times and optimized the network a few times.  Any advice to help out?