Continuity mistake: According to the previous film, Thor: The Dark World, Asgardian kings live approximately 5,000 years. (If I want to be cautious here, this statement is only valid about Odin and of unknown validity about other Asgardians.) But in this film, Thor says Odin fought Surtur 500,000 years before.
Continuity mistake: In scene when Revengers are escaping through Devil's Anus, it is revealed that the ship has no weapons because it's a "leisure vehicle." Later when they appear to help the people on the rainbow bridge, they open fire with a cannon mounted in the vehicle.