I’m using FP3 in USA on Metro.
Sometimes I my phone enters this state where any calls whether incoming or outgoing seem to connect but without audio going in either direction. I believe it connects because incoming calls will have ringing on the outgoing phones speaker, and the call timer starts on my FP3 when a call connects, but I have dead silence.
Restarting the phone fixes this problem.
I play this game called Fallout Shelter that behaves somewhat strangely. When I lock my phone while the game is on and then unlock it, the game comes back but not before showing the home screen with the icons reoriented and the colors and resolution somewhat changed. I don’t know if this app may be causing the sound problem but it’s the only other thing that is strange on the phone, and I have a feeling that the sound issues has ever only happened after using the game app.