Every so often during a live match one of my pieces will be missing. For example if i am white b1 will be vacant and g8 will have a white knight sitting pretty. I can sometimes grab this knight and place it on c3 successfully but not always. Has this happened to anyone else?

yes on numerous occasions! but usually i just reload the page never to see it again in that match

I haven't tried refresh yet. Usually the black knight is hidden beneath it's wayward cousin and reappears. This problem is especially troublesome when I'm in time trouble.

Are you using Chrome by any chance?