An Ill Wind - S3-E8
Revealing mistake: After they break out of the basement, Iola remains down there, with no indication that she is coming up. However right after we can see her skirt on the staircase, waiting to make her entrance later in the scene.
Grandma USA - S3-E12
Plot hole: Thelma never mentions the song name she will sing at the pageant, as she had no idea she needed a talent, thus she couldn't tell them ahead of time, but they still start to play the right one for her.
Birthright - S3-E18
Continuity mistake: In this episode Vint says he was born on April 23. But in the lottery episode when Mama picks numbers with Iola she says Vint was born in March.