I have heard stories of candidates that are asked to correct and resubmit their thesis after their viva. Resubmission is a formal process; it can mean that the candidate has to have a second viva. It could be that the thesis was incomplete or in some way “not right”. It could be that on that occasion the candidate needed to say something in particular – but didn’t.
It could be this or it could be that, but one thing that is certain is that the “second chance” of resubmission and a second viva is incredibly rare. It happens and it happens for specific reasons. If you’re concerned about it in advance of your viva it might help to read the regulations for your university or talk to your supervisor to see if there is anything in your work to really be concerned about.
Again, it is incredibly rare for all of this to happen. While it might help to find out more about resubmission and second vivas just in case, it’s probably better that you focus on other things instead: your research, your thesis, your preparation. These are certainties that can help you to succeed – a far better focus than a hypothetical that will only serve to distract you.