Factual error: Towards the end of the movie when Ally is in her hallway looking at Jack's old concert tour posters hanging on the wall, the poster closest to the camera says "Washington State Fair" and a 2011 date. Unfortunately, that fair did not get that name until 2013. Before that, it was called "The Puyallup Fair" (officially named the "Western Washington Fair"). Locals still call it "The Puyallup Fair" to this day.
Revealing mistake: Jack and his brother are driving in a truck and the speedometer shows zero.
Continuity mistake: While Ally is in the tub talking with Jack, he says that his father has more talent than Ally. She drinks from the glass and the level changes between shots.
Continuity mistake: The first time we see Jackson rehearsing, his brother comes to the first row to talk to him, always with his right arm down. There's a brief shot from a different angle where his arm is suddenly up. Then back to the previous angle where the arm is lowered for the rest of the scene.
Continuity mistake: When Ally gets on the plane to go see Jack she is wearing sneakers (you can see them when she lays on the couch in the plane) then in the next scene when she's on stage singing with Jack she's wearing shoes with a high heel. (00:34:45 - 00:42:10)
Continuity mistake: When Jackson surprises Ally visiting her in her bedroom, she is lying down with her hair covering her forehead. When the angle changes her forehead is uncovered.
Continuity mistake: When Jackson asks Ally to go onstage and play, her hair is brushed with a bang falling on her forehead. Shot changes to Jack watching her with a live video playing of her behind, and now her hair is messed up. Angle back on Ally and it's neat as before.
Continuity mistake: When Jackson visits Ally in the Bleu's dressing room, she puts her left hand to her head, but in the immediate opposite angle it's down.