After connecting the device the WiFi worked fine but a separate problem came up. A computer (Windows 10) that's connected via Ethernet to the same network (it's not connected to the extender but to the router itself) has connectivity issues. 
"Ethernet doesn't have a valid IP"

Thought it was a system issue so we did any troubleshooting step imaginable. Nothing worked until we pulled the WA860RE out of the wall. We thought somehow both devices had accidentally gotten the same IP. We reset it and tried again checking that both have different IP addresses which they had. Everything worked fine until one day later where we had the same problem that only got fixed by pulling the repeater out again. 
Does anyone know why this happens since both of them are connected separately and should work independently from one another. 
and is there a fix?