I have a 3 Mesh System using Deco P9 and needed to add on another unit but I cannot find another unit so I bough an S4.   I connected it today and I have had nothing but issues with the entire mesh system.  When there is no activity the S4 starts blinking red and I will not get any internet through any device, I have to disconnect my internet and restart it before everything works again. The S4 is an add on and not my main unit.  Why is this happening?