EX7700 X6 AC2200 Tri Band Mesh extended. Connectivity issues

I have had the extender for over a year with minimal issues. Recently it has started playing up. It won't show up or if it does won't allow my devices to connect. Sometimes it give no internet connection or keeps saying invalid password. 

I have restarted the device a number of times for it to work for a small time before the same issues occur again. I have also reset the device and done new set ups. Again same issues. The fireware is up to date.

Any ideas how I can fix this. Without this, I have no or poor connection in my loft as the router won't reach that far. 

Thanks