Nerves
Nerves are normal! An interview is not a normal social situation - you are meeting people who you may have not met previously so you and they are unsure quite how to act. Being nervous before and during an interview are normal and can actually help you to perform better.
A more informal conversational meeting can help to settle nerves but this may not be possible and panel style interviews do not give the opportunity to have a more intimate discussion with one person so accept that you may have a limited opportunity to break the ice in those situations.
Nervousness can have 2 main effects - either your mind goes blank and you cannot think of anything to say in response to a question OR you can speak too much and not allow the other person back into the conversation.