Call Hanging Up?

Hey there,

So recently my boyfriend and I have been having problems when we are on the phone. For him, it says I have hung up on him yet I am still on a call with him. It sounds as though he is muted of course. Everytime this happens he will call me back and it will have the options: Decline, Hold & Accept, or Accept & End the call. It happens every night around 11:30-Midnight, then on his end the phone hangs up around 2-2:30am. Has anyone else had this issue or know how to resolve it? It’s really bothering us. Both of us are up to date for iOs. I have the 11 Pro Max, he has the XR.