Does anyone know how to cure a problem with the Sonos iOS app not being able to switch to the base wifi network when moving from coverage of an extender? Seems only to occur on iPhone (OK on MacBook) . The range extenders a TP-Link power line extender with wifi enabled and works fine with everything else. One Sonos unit is directly connected to the base modem and the modem (a BT hub) has smart set up switched off. The problem only occurs going from extender to base network not from base to extender.