As You Were - S6-E15
Audio problem: When Buffy has just killed the Suvolte demon and Riley is found out to have not told her it was a tracking only mission Sam says something like 'If we weren't under time constraints, I'd rip you a new one.' Riley then says 'Stand down soldier.' Buffy asks Sam, 'Is he your boss?' And Sam replies 'He wishes. We better regroup.' But her lips to not move when she says they have to regroup. You can see her mouth on screen and she is just smiling, not moving her lips at all.
As You Were - S6-E15
Audio problem: When Buffy and Riley are fighting the Suvolte demon at the dam, Buffy calls out Riley's name at some point during the fight. Her lips don't move.
Chosen answer: He had larangitis and because of the shooting specifications they had to have him shoot the scene with a bad throat, they then re-recorded his lines and dubbed them. At various points during the scene and indeed the episode you can see him touch his throat or rub it.