Be sure the router and extender are by the same maker and the firmware in both is current. If it still fails and requires a new WPS connect, it's defective.
The extender works great most of the time, but when I leave the house with my devices (ipad, iPhone) and I come back they do not connect automatically with the extender. They connect to the wifi in the back of the house(weaker signal, hence extender) but if I want to connect to the extender again I have to press the WPS button on the extender and the router in the back of the house. Or I have to restart the extender. Is there any way to change this? It is pretty inconvenient to do this every day, several times a day sometimes. Thanks for any advice!