I have that too, probably because when we meet someone we don't know, we try not to stutter and not make an impression that we have this problem, while with close friends and family they already know we stutter and it's easier. because we don't try to hide it so much. I'm trying to convince myself to try to walk up to strangers and try talking to them but i just can't, i start to have a lot of anxiety even when i think about it.