@robbiek 

Thank you for joining the community,  if range extender goes into reboot loop, you could try a factory reset for it

• RESET: With the extender powered on, use a pin to press the RESET button (pinhole) until all the LEDs flash once.
• Try a different power socket 

If still the same issue, it is recommended to reach local support or retailer to check device warranty, you could get the product SN, proof of purchase when contact the support.