@keratalay 

While waiting for source signal selection to be implemented, you could try a workaround. According to TP Link Support, what they are saying on multiple threads in this forum related to similar issues you experienced with E4, Satellite Deco will stick with Main Deco as long as signal between them is above threshold.

So, turn off two other Decos, leaving Main and one from Satellites you want Main to be connected to it, but it does not. This remaining Satellite Deco will have no choice but connect to Main Deco. 

Then, check quality of signal between these two Decos, see "Signal Source" in Deco app. If it is at least two bars they'll keep staying connected, TP Link Support tells us.

After that, power on remaining Decos.

This is, of course, not ideal solution, but if you want to keep new E4 you bought it might work for you for now.

@Alexandre. 
 

Thanks for the reply. This worked for a while but after i activated others. I ran into my original problem which is ; on my tv and mac i dont seem to have a problem but on the phone most pages dont respond. I switch to gsm 4g same page opens immediately. And after that i restart all routers and source signal again seems messed up. I'm worried even if there is a fix my problem will persist