EX3800 wifi range extender keeps disconnecting

I have an EX3800 range extender. I can connect it to the router but the wifi keeps disconnecting almost every minute. The connection again shows "limited" or it just disconnects itself completely, even when the extender is in the same room as the router.

Using my mobile as a hotspot (instead of using the router) the extender works fine.

I have the issue with a Windows 7 laptop and an android phone.