There's a similar bug on v2, and I've lost a game because of it. It sometimes doesn't recognize that it is your turn, even though it is and the board shows that. It has only happened twice to me in 2.5 years, so I haven't reported it.
Thanks for the fullscreen tip, btw! I'm gunna have to try it.
So I had the V3 enabled and going through my online (not live) games and delivered checkmate with white in one of them (http://www.chess.com/echess/game?id=100870404 in V2). I saw 2 errors in red in quick succesion on top of the screen and did not snapshot it as I thought these were hickups that would not have major consequences.
Unfortunately, when I reloaded the page I saw the game was stuck where it thinks it's white's move but I can't make it for some reason (maybe because the game is over?). Since then I switched back to V2, and the game is stuck in the exact same way.
So there really is a second bug here: if for whatever reason chess.com expects a move to be made but this move has already been made and even if the game is over, the user should not be left in this silly stuck situation. It is probably something that should be fixed, at least as a work around to the original bug so that people don't loose on time out when they really should have won. I submitted a bug report separately.
Note I don't really mind to loose a game (very occasionaly) on a bug (though many people I suspect will disagree), but I don't want to be kicked out of the quick knock out tournaments because of a time-out that is not my mistake.
Thanks for following up with this. I am begining to warm up to the V3 UI. Looks especially good on tablet or on PC in full screen mode (F11).