N300 (WN3000RPv3) WiFi Range Extender Client link keeps dropping

Hi I have a N300 range extender (WN3000RPv3) which I bought a couple of years ago and used successfully pretty much without interruption. On 15 January I changed broadband provider which also meant a change in router. In order to get the N300 extender to talk to the new router, I had to do a factory reset and then update the firmware. It took a while and I had to update it twice to get it to work. The unit is now working, but it intermittently drops the client link - when this happens, the client link light goes off completely and nothing can connect to the extender. Switching the extender off and on again fixes the problem, but it would be useful to know if there's a more permanent fix. The signal between router and extender is fine - quite strong. The router is a Technicolor TG588V v2. Any ideas appreciated.