Often when I receive a call, after a half or one minute my mic goes on mute. It only happens when I receive the call so far. When this happens, I have to unlock the phone, and select the ongoing call which is somehow gone to the background, and it is automatically unmuted. The first picture shows normal calling, when everything is OK. The second is when the mic goes muted (notice the mute icon in the upper right corner).
In "I have to unlock the phone, and select the ongoing call which is somehow gone to the background, and it is automatically unmuted." this line is confusing do you mean "it is automatically muted" ?