Hello everybody

I recently bought the Deco M4 (3 pack) to extend the WiFi signal in my house from the first floor (ground floor), where the main router is located, all the way up to the 3d floor. First day, I set everything up, one deco for each floor with the main deco directly connected to the main router downstairs through a cable, and they all run like a clock but ever since the second day of use, the two satellite decos on the 2nd and 3d floor keep disconnecting from the main deco with their LED light blinking red. 

Although it mostly happens at random moments, I have also noticed that when I connect my laptop to the 3d deco via an ethernet cable it seems to make things worse. The distance between the decos is ridiculously small and the signal is normal (2 bars),  I made sure of that myself so the constant disconnection definitely isn't because of the distance. I even tried changing the operation mode from router to access point but that didn't help much either (I'm still not sure about whether I should have it in router mode or access point mode by the way). 

Finally, I have been told by a tp-link representative that I should probably turn off the WiFi signal from the main router to avoid any interferences. I can't begin to describe the cons of permanently disabling the WiFi from the main router but even when I tried it, it didn't help at all. If anything, I lost my Internet connection altogether even from the decos. 

So, if anyone could help me solve the problem with the constant disconnection, I would greatly appreciate it. Thank you very much in advance.