I have an Asus Max Pro M1. Recently I have discovered the phone does not work properly . My family kept asking me why I dropped my calls too early that they could not answer. Later, I realised that when phone of the called party was ringing, my phone returned with a "engaged" sound and I dropped the call. I have done several experiments on the issues. Some conclusions drawn are as follows: 1. The problem happens constantly on some telephone numbers of called parties, no matter which SIM slot my SIM is using; 2. When my SIM is used in other handsets, it works perfectly.