When Anna takes Rosamund and Lady Mary upstairs to walk in on Lord Hepworth and Rosamund's maid, Shore, Anna is seen first opening the door, and then entering the room with Rosamund and Mary. She is present throughout the scene.
However, after the confrontation with Hepworth, when Rosamund and Mary turn to leave, Anna is still seen behind them, about to leave the room as well and close the door behind them.
But when Mary and Rosamund are seen in the hallway a moment later, Anna, who was just seen about to close the door and walk away from them down the corridor has completely disappeared and is nowhere to be seen.
The door can also be heard being pulled shut as Mary and Rosamund are seen standing in the hall, however Anna, who closed the door is seemingly nowhere in sight.
In the scene where Thomas meets Lord Grantham after his dog has been returned, Thomas's collar is shown undone and hanging loose. It then disappears entirely, then reappears, then disappears and then appears tucked away on the other side of his coat.