@Ezekielv 

Hi, welcome to the community.

May I know how many Deco E4 do you have?

Are you able to help me check the wireless signal strength(dBm), such as 5 meters away, 10 meters away via the Wi-Fi analyzer App?

Since E4 has 2.4ghz and 5ghz, in case one band had the problem, could you please test the signal one by one?

By the way, do you still remember what is your original firmware before 1.5.4, like 1.5.1 or 1.4.3?

Thank you very much.

  @Ezekielv 

Hi, thank you for getting back to me.

The recommended distance for Deco E4 would be about 10 meters in order to have a good speed.

I believe the firmware is not the problem.

If your house is quite large, one more Deco E4 would be helpful a lot.

  @Ezekielv 

Hi, 5-10 meters is a very suitable distance to get a good signal and internet speed, and when it comes to 15-20 meters, you will still get Wi-Fi signal one or two bars but the connection rate will reduce with the distance. The speed would not be as good as 5-10 meters. In the real network situation, the distance is not the only factor that affects the wireless coverage and connection rate, such as physical barriers(concrete walls and trees, etc.)