Factual error: The American soldier on the balcony is waving a 50 star flag. (01:30:06)
Other mistake: When Rosie plays her husband with ashes on her face she touches the tablecloth but it does not get dirty.
Continuity mistake: Towards the end of the opening credits, when JoJo and the rest of them are first running through the woods. The swastika is reversed and everything is on their right arms. At the end of the credits, the badges are on the left arms.
Audio problem: Towards the end Fraulein Rahm sends a child towards the Americans after pulling the pin on a grenade attached to him. He runs offscreen but no explosion is ever heard.
Suggested correction: So the grenade was (thankfully) a dud. Considering they were wearing paper uniforms, it isn't unreasonable to assume they didn't have the highest quality equipment.
Continuity mistake: After Jojo finds Elsa for first time he talks with Adolf in his room, he recharges on the wall then moves a little bit but suddenly is 1 or 2 steps from the wall.
Continuity mistake: When the swimming pool scene is about to end, Finkel raises his arm and hand. A shot later it's lowered.
Continuity mistake: Jojo's mom makes him look at the people hanged in the public square. When they turn around and walk away, between the two shots there are clear changes in position in passersby in the background. (00:20:30)
Continuity mistake: During their first night at the camp, Jojo and his friend are talking while they play with their knives. During the scene the knives change position between cuts (blatant especially when they mention the brussels sprouts or when he rolls to the other side to sleep). (00:08:40)
Factual error: Russians and Americans never fought in the same battle against Germans.
Suggested correction: The film does not depict Russians and Americans fighting in the same battle. Jojo's friend, Yorki, tells him that America is coming from one direction and Russia from the other, but also says they are being attacked by China and Africa. He is a child and doesn't really know what is going on. We don't see any of the attackers until after the battle is over, at which point they all appear to be American.