@iAmCtrl 

Hi,

Do you mean the wired devices cannot get internet when wired connect to the range extender?

Please also connect to the main router directly and check if it can work normally.

And could you please provide the topology of your home network? Is it like main router)))(((RE? Is there any other devices in between?

You can also use speedtest.net to test the real speed you get, and compare it with the speed you get from the main router directly.