My four year old is always extremely unsettled whenever they first interact with a guest.
It doesn't matter if it is another child who has played with many times before or an adult.
It also doesn't matter if it is at our house or outside somewhere like a park or restaurant.
There is usually 5 - 10 minutes of him trying to bury his head, not greeting the person, trying to pull us away from the person and quite often there will be tears.
This usually ends in him going to time out and once he has come out he is completely changed. His head will be up, he will be extremely friendly and talkative.
My wife and I have guests over quite regularly, so it is quite common for him to be around different people. But it happens almost every time.
I'm assuming it's some sort of anxiety with guests, so is there anything we can do to reduce this? We always tell him in advance when someone is coming.