Continuity mistake: When Samantha is in the bathroom holding up two sample paint chips, in the first shot Sam is holding up the yellow in her left hand and the blue in her right hand, but in the next shot they've switched and are in the opposite hands, just as Jay arrives with the coffee.
Outlook Good - S3-E1
Continuity mistake: Peanut the dog disappears in the shots taken from behind the old lady. (00:31:58)
Ghost Light - S3-E6
Continuity mistake: When the three are arguing in the dressing room, Oliver says, "I don't care," then turns and wipes most/all of the lipstick writing off the mirror, leaving a load of messy smears behind. In the shot of Oliver when he says, "in a few weeks..." the mirror is behind him, with no smears. At the end of the scene as Mabel says "I'm done" and storms out, the mirror is very smeary again.
Continuity mistake: Harper grabs her glass of wine, but a shot later, it's back on the table. (00:36:52)