Continuity mistake: The egg timer in the jail is about to run out, but when Dale runs over to it and tries to turn it over, there is more sand in it than before.
Revealing mistake: When Biro stabs the Imperial soldier with his sword, it's obvious that the sword is angled to miss his body.
Continuity mistake: There are a couple of instances in the movie where the models do not correspond with the actual sets. When Klytus arrives at the Hawkmen city he lands near the top of the city. Yet in that very hall there is a pit with a deep void underneath. Such a room could only exist at the bottom of the city. Also, when the Hawkmen start to land on Ajax, its engine section appears to be missing.
Continuity mistake: Several small meteorites are shown falling to earth. Two of them land in water, but only one of them creates steam.
Revealing mistake: When the Hawkmen city is destroyed, you can see the lower portions of it wave about, revealing that it is in fact a model.
Other mistake: The scenes with Flash and Aura in the shuttle are a complete mess. She tells him that the left lever controls direction, the right controls the altitude. When they are passing the planet Aquarius, she tells him to take a left turn over Fridgia. A) They are passing Aquarius at the time, not Fridgia. B) He moves the right lever instead of the left lever. C) The craft doesn't change direction or altitude and even if it had moved left as supposed to, they would have ended up crashing into Aquarius. The scene when Flash wants to talk to Dale is even worse. He pulls down the left lever to dive into Fridgia. It is the wrong lever. Then when he pulls back up, he correctly uses his right hand, but the right lever is already in the up position as seen in the previous shot.
Other mistake: During the battle for War Rocket Ajax, an Imperial soldier is shot by a Hawkman, but falls down after he should have done.
Other mistake: When Flash and Vultan are watching the battle unfold on War Rocket Ajax, the rocket is seen moving forwards, with engines flaring, even though the captain has given the order for the engines to be stopped.
Revealing mistake: When Flash is rescuing Barin from falling into the void, he rubs against one of the spikes and it bends as if made of rubber.
Continuity mistake: When Dale escapes and fights the guards, the editing is really awful: first she knocks a guard, who later on changes positions. Then she walks away, leaves her shoes on the floor, and hides against a wall, but after a brusque cut she appears somewhere else, the shoes are 15 meters away and the guard from before lies in front. (I guess that some of the fighting in between was deleted.)