@Chavdar 

Hi, when Deco E4 stopped working, have you checked whether the internet service from the modem is still active?

If not rebooting E4, will the internet service restore automatically?

Usually, If E4 stays white, it should still be online. How did you find out E4 stopped working?

And it is also suggested to refer to this link for detailed troubleshooting(case III is more appropriate）:

Fix unstable connection when connected to the Deco network

Thank you very much.