When Wilma Deering gets into her fighter on board the Draconia, her helmet is marked 'Col. Deering' on the right side. In the subsequent shots during the fight, it's unmarked. A similar thing happens again close to the movie's ending: When picking up Buck Rogers, Theo and Twiki on the Draconia, there is one shot of her with her helmet being marked 'Col Deering' - this time on the left side - whereas in all other shots the helmet is clean.
When Captain Buck Rogers fights Tigerman in the launch bay of the Draconian flagship, the actor is very dissimilar from the one in the rest of the movie.
When Buck Rogers is in the ruins of Chicago and the graveyard, the likelihood of the signs in the streets and the gravestones still being legible after 450 years is nothing. Weathering would have totally erased the words from the signs by then.
Although two starfighters ascend from Earth to intercept Buck Rogers' spaceship, we see four blips representing four starfighters on the "big screen" in the control room.
At 1:14:00 a Draconian bomber explodes inside the Draconia's hangar. A technician who is working on the wing gets launched into the air by the blast. As he falls the ship, which is supposedly a sturdy structure made of metal, wobbles very noticeably.
At about 1:12:00, right after Buck tells Theo and Twiki that they have to find a communicator on their own, a Draconian guard is heard shouting "Commander Kane, we found a guard unconscious in bay three!". It cuts to Kane listening to two of the guards. The Draconian bomber they stand in front of is a very obvious flat cutout.