LG4 - Not receiving incomming calls

The phone will sometimes receive the incoming call and other times not.
No issue with signal.
Went through all the setting as used on my other LG4.

I tried a few times calling the phone.
No indication or sound for the incoming call.
Received a sms notification regarding the missed call.

Later the same day, called the phone and it was ringing.
10 min later, another test call - no rining (same problem.)

Did the software updated still same problem.

Bring it to the carrier. There can be many causes, some caused by problems with the carrier.