Network Extender Connectivity

[HERSEI2]

My network extender has worked fine for over a year-suddently, none of my phones are connected to it-no change in phones, internet, etc.  All 4 lights are blue, I've powered off all devices, still won't connect.  What's up with that?

[jav6]

What model phone(s) aren't connecting? Which model extender is it?  Is it possible the phones have WIFI calling activated and that is taking precedence? Is it possible an outside signal is now more powerful than the extender's signal? Are the phones able to make calls at all at your location?  If it is the 3G Extender, is it set for 'Open Access' or 'Managed Access'?