@Mikolertesx,

The Deco E4 is not sold in the United States, so therefore depending on what region you are located, there may be an incompatibility between the regulations for wi-fi. If you are using the Decos outside of the US, make sure that your Deco M4 is not a US model. 

Otherwise, I would recommend posting to our global forums:

https://community.tp-link.com/en

as they will have worked with this deco model before and may know if any settings are recommended to be changed. Our deco nodes, when used as recommended, will work together to create a reliable mesh network