After initial pairing of adapter and range extender through adjacent electrical sockets, and moving the extender then to a different electrical socket, pairing only succeeds when staying below the second floor. Pairing is impossible from any electrical socket of the second floor onwards.

When pairing succesfully, the powerline led on the extender briefly lights up, goes dark again, and then after some seconds lights up again and stays lit. On the second floor, where pairing does not work, the powerline led also briefly lights up, but then stays dark afterwards. 

The strange thing however, pairing on the second floor was possible until some days ago. No changes were made to the Internet modem confguration. And no interventions were carried with the electrical wiring of the house. Without it, the product is useless to us, since it needs to get Internet access to the second floor office. 

Did the extender become less performant? 

Thanks for any advice!